SiO2 /WO3 /ZnO Based Self-cleaning Coatings for Solar Cells

SiO2 /WO3 /ZnO Based Self-cleaning Coatings for Solar Cells | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article SiO2 /WO3 /ZnO Based Self-cleaning Coatings for Solar Cells Ozcan Koysuren, Klodian Dhoska, Hafize Nagehan Koysuren, Irida Markja, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3704926/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2024 Read the published version in Journal of Sol-Gel Science and Technology → Version 1 posted 10 You are reading this latest preprint version Abstract The accumulation of pollution and any kinds of contamination on the glass cover of the solar cell affects the efficiency of the photovoltaic (PV) systems. The contamination on the glass cover can absorb and reflect a certain part of the sunlight irradiation, which can decrease the intensity of the light coming in through the glass cover. With the study, it was planned to develop self-cleaning coatings for the PV systems. It was aimed to prevent or reduce the contamination-induced efficiency loss of the existing PV systems. In the scope of the project, SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO composites were coated from their solutions on the glass substrates using a dip-coating technique. WO 3 was selected as a photocatalyst semiconductor. Under the UV light irradiation, WO 3 could absorb the photons of the UV light, generating the photoinduced charge carriers. The photoexcited charge carriers provide both the photoinduced hydrophilicity on the surface of the coating and the photocatalytic degradation of the organic contaminants accumulated on the surface of the coating, which allows water droplets to spread and flow on the surface of the cover glass to remove the contaminations. However, the recombination rate of the photoexcited charge carriers on the WO 3 film was high. In order to suppress the recombination of the photoinduced charge carriers, WO 3 was coupled with SiO 2 and ZnO. Both of these semiconductors improved the photocatalytic activity of the WO 3 film. Although SiO 2 has superior features in terms of the light transmission, it was not very effective under UV light as a photocatalyst alone. The widely preferred photocatalyst ZnO was added into the composite film structure to enhance the photocatalytic activity. The self-cleaning mechanism of the film coatings on a solar cell was investigated through the photocatalytic dye removal efficiency on the as-prepared film samples. There was a slight decrease in the light transparency and the solar cell efficiency because of the WO 3 content of the composite film. On the other hand, coupling the SiO 2 /WO 3 film with ZnO enhanced the photocatalytic activity, and it suppressed the reduction effect of the WO 3 phase on both the light transparency and the solar cell efficiency. The photocatalytic dye removal efficiency was increased to over 90% after 240 min of UVA light irradiation. In addition, the solar cell coated with the SiO 2 /WO 3 /ZnO film provided almost the same solar cell efficiency as the uncoated solar cell. The water contact angle measurement also exhibited the photocatalytic degradation of the model contamination on the glass cover of the solar cell under the UVA light irradiation. Self-cleaning coatings solar cell photocatalytic activity hydrophilic coatings Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Highlights Coupling WO 3 with SiO 2 and ZnO provided enhancement in the photocatalytic activity. The photocatalytic dye removal efficiency was improved to over 90% with SiO 2 /WO 3 /ZnO film under UVA light irradiation. The light transparency of the SiO 2 /WO 3 /ZnO film in the visible light spectrum was almost 5% lower than that of the cover glass of a solar cell. There was a decrease in the water contact angle due the photocatalytic degradation of the model contaimination on the film coating under the UVA light irradiation. Introduction Self-cleaning coatings are found in a wide variety of applications such as solar cell panels, electronic and optical device panels, window glass, textiles and paints. Self-cleaning coatings contribute to reducing the efficiency lost of the solar cell, cleaning costs and maintaining stability of all surfaces. Self-cleaning coatings fall into two categories: hydrophobic and hydrophilic coatings [ 1 ]. A surface with a water contact angle greater than 90° is considered as hydrophobic. On the hydrophobic surfaces, water droplets take the shape of a sphere and clean the surface by rolling the formed droplets [ 2 ]. On the other hand, for hydrophilic surfaces with a water contact angle less than 90°, the self-cleaning mechanism occurs by photocatalytic degradation of the pollutants under UV radiation and then the removal of the contaminations formed on the surface with water. Semiconductor photocatalysts such as ZnO and TiO 2 can be added to the surface coatings to make the surface hydrophilic [ 2 , 3 ]. Photocatalytic degradation, which is part of the self-cleaning process on hydrophilic surfaces, is the decomposition of organic compounds into small molecules such as CO 2 and H 2 O. In photocatalytic degradation reactions, light with energy equal to or greater than the optical band gap energy of the photocatalyst can be absorbed by the photocatalyst. In this case, electrons in the valence band of the photocatalyst are excited and transferred to the conduction band. The electron vacancies, called as holes (h + ), formed in the valence band of the photocatalyst, which can oxidize the surface adsorbed water molecule and turn it into a hydroxyl radical; the electrons excited to the conduction band can reduce the surface adsorbed O 2 molecule and convert it to a superoxide radical. Both active radicals formed allow the degradation of organic pollutants adsorbed to the surface of the solar cell panel [ 2 ]. In the literature, different semiconductor photocatalysts such as TiO 2 [ 4 ], ZnO [ 2 ], KWO 3 [ 5 ] and Bi 2 O 2 CO 3 [ 6 ] have been used to develop self-cleaning coatings based on the photocatalytic activity. Several studies from the literature have been summarized on Table 1 . Self-cleaning by semiconductors takes place through the photocatalytic and the hydrophilicity mechanisms. The photocatalytic mechanism results to degradation of the polutions while the hydrophilicity mechanism laminates the water droplets on the surface to wash the degraded pollution, preventing the adhesion of the pollutants on the surface. In literature, Khorshidi and his coworkers (2021) measured the water contact angle on the acylic/ZnO coating, deposited with a model pollutant (stearic acid). Under the UV light, the stearic acid molecules degraded into H 2 O and CO 2 . H 2 O as a degradation product might decrease the water contact angle of the coating about 22° in 135 min. Hence, a decrease in the water contact angle might exhibit the potential of the photocatalytic activity and the cleaning of the coating surface [ 2 ]. Table 1 Self-cleaning surface studies based on the photocatalytic activity from the literature Coated Surface Photocatalyst Results Building material (concrete surface) [ 6 ] Bi 2 O 3 , Bi 2 O 2 CO 3 , BiOI, BiVO 4 , BiPO 4 49% pollution (model dye) removal after 3 hours with Bi 2 O 2 CO 3 Polymer (PMMA) [ 4 ] TiO 2 Approximately 80% dye removal after 3 hours Glass surface [ 5 ] KWO 3 29% dye removal after 2 hours Cement mortar [ 7 ] TiO 2 /ZnAl layered double hydroxide Reduction in water contact angle about 90° in 210 min. Glass surface [ 8 ] WO 3 /TiO 2 3.6% achievement in energy output gain after 8 months Glass surface [ 9 ] TiO 2 /SiO 2 Reduction in water contact angle from 90° to 20° in 70 h. Glass surface [ 10 ] Cu-TiO 2 , Ag-TiO 2 , Fe-TiO 2 and Co-TiO 2 77%, 74%, 76% and 69% pollution (model dye) removal after 2 hours with Cu-TiO 2 , Ag-TiO 2 , Fe-TiO 2 and Co-TiO 2 Glass surface [ 2 ] Acrylic/ZnO Reduction in water contact angle from 90.2° to 68.1° in 135 min. Glass surface [ 11 ] TiO 2 /Kaolin 65% dye removal after 210 min. The change in hydrophilic property of a solid surface with light radiation is related to the change in surface energy. There are different assumptions about determining the reasons of changes in surface energy at the atomic level. According to an assumption, the hydrophilic property of the solid surface increases with the contribution of organic pollution products that decompose under light. This is explained by the formation of metastable nano-sized hydrophilic regions on the surface due to the transport of the photogenerated electron-hole pairs to the solid surface. The second hypothetical mechanism of the photo-induced hydrophilic transformation of a surface is related to the thermal effect of light. This effect causes water bound by weak bonds in the outer layers of the solid surface to separate from the surface. Thus, the surface energy and thus the hydrophilicity of the solid increases. Then, water molecules spread on the solid surface, forming a film layer. Re-adsorption of water restores the initial structure of the hydrated layer and thus reduces the surface energy [ 12 ]. The sun provides free heat and electricity for real-life applications. In addition, the solar energy is environmentally friendly and it does not produce any emissions. For this reason, solar energy could be the most suitable and sustainable solution to the energy crisis of the World. However, several problems hinder optimum power harvesting from the photovoltaic (PV) modules. Dust accumulation on the surface of the PV module has been known as one of the crucial problems of the PV systems [ 13 ]. As it is known, the light-permeable surface of the solar cell can be easily contaminated due to the adhesion of dust, organic pollutants and inorganic particles. Accordingly, the light transmittance of the surface and the light absorption of the solar cell could reduce. In addition, cleaning the contaminated surface requires extra labor and money. There is also the possibility of scratching and damaging the surface during the cleaning. Therefore, the removal of the surface adsorbed polution from the PV panel is of great importance [ 5 ]. There are three different self-cleaning methods, applied to clean the PV panels. Electrostatic, mechanical and coating methods are among these techniques to clean the surfaces of the PV panels, which are exposed to the outdoor conditions. The electrostatic method throws out the dust from the surface through the electrostatic wave. The mechanical method consists of four techniques, robotic method, air blowing method, water blowing method and ultrasonic vibration method, to expel surface adsorbed dust. The coating method technology is based on forming a thin layer of film coating, which can be either hydrophilic or hydrophobic. The hydrophilic coating reduces the surface pollution through a photocatalytic degradation reaction, while the hydrophobic coating rolls the water droplet to remove the pollution from the surface of the PV panel [ 13 ]. The accumulation of the pollution and its effect on the effiency of the PV cell depends on the tilt angle of the PV system, the exposure duration, the climate conditions like the wind condition, the pollution density and the surface material of the PV system [ 9 ]. Tungsten oxide (WO 3 ) has been utilized as a photocatalyst for the degradation of the organic pollutants under the UV light irradiation. WO 3 as a photocatalyst has important features like nontoxicity and chemically stability. Also, WO 3 exhibits high resistance against acids and it has high photocorrosion resistance [ 14 ]. Due to the specified properties, WO 3 is preferred in gas sensors, photochromic and electrochromic device applications. WO 3 can also be thought as an appropriate anode material in the photoelectrochemical water splitting reactions [ 15 ]. Although WO 3 can absorb the entire range of the UV light spectrum, the recombination rate of the photoinduced charge carriers, generated on WO 3 , is high [ 16 ]. Forming a p-n heterojunction within the composite structure is a best solution to suppress the recombination of the photoinduced charge carriers and subsequently to enhance the photocatalytic activity. When n type and p type semiconductors are brought together to provide a stable contact, an electric field will be generated between the semiconductors, providing the reverse transfer of the charge carriers. The electric field provides the separation of the photoinduced charge carriers between the semiconductors [ 17 ]. In literature, several studies have been conducted to promote the separation of the photogenerated electron-hole pairs on WO 3 such as WO 3 /TiO 2 [ 18 ], WO 3 /SnS 2 [ 19 ], WO 3 /SiO 2 [ 20 ], WO 3 /CdS [ 21 ]. By coupling WO 3 with another semiconductor possessing a valence band edge and a conduction band edge more positive or more negative in level than the valence band edge or the conduction band edge of WO 3 , the photoexcited holes or electrons can move between the bands of the semiconductor and WO 3 , suppressing the recombination of the photoinduced charge carriers on the semiconductor and WO 3 . This event can enhance the photocatalytic activity [ 22 ]. In the scope of the study, WO 3 was combined with SiO 2 in the composite film structure. The sol–gel technique, known as one of the most efficient methods to prepare the composite films, was applied to prepared SiO 2 /WO 3 composite films. The sol-gel technique is relativelty simple and a low-cost process when compared with the deposition methods applied under vacuum [ 23 ]. Also, ZnO was added into the composite film to enhance the photocatalytic activity and subsequently the self-cleaning property. The application potential of SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO films as a self-cleaning coating on a real solar cell was studied. There were some challenges to be removed before the self-cleaning coatings could be used in practical application. ZnO and WO 3 exhibit the light-induced superhydrophilicity and these semiconductors exhibit photocatalytic activity under UV light irradiation. When exposed to the UV light, ZnO or WO 3 can degrade any kinds of organic contaminants or pollution adhering to the surface of the glass cover of the PV panel. The UV-induced superhydrophilic property of ZnO and WO 3 allows water droplets to spread and flow on the surface of the cover glass, contributing to the self-cleaning process. Combining the self-cleaning process and the photocatalytic activity within a coating is of great importance in terms of the solar energy technology [ 23 ]. However, ZnO or WO 3 coatings on the glass cover of the PV panel could reduce the transmittance owing to their relatively high refractive index (n = 2 for ZnO and n = 1.9 for WO 3 ) compared to SiO 2 (n = 1.5) [ 24 ]. On the other hand, SiO 2 with a low refractive index and low surface scattering is beneficial and effective in improving the light transmission for the glass cover of the PV panel. In addition, SiO 2 film exhibits hydrophilicity and self-cleaning properties owing to the presence of hydroxyl groups in its chemical structure [ 23 ]. However, the superhydrophilicity of a SiO 2 film coated on the cover glass of the PV panel may reduce in time owing to deposition of dust and organic pollutants, and the photocatalytic activity of SiO 2 is low [ 24 ]. The optimization of the coated film in terms of the specified features is a significant and a detailed study was conducted to achieve a balance between the specified properties. In literature, there is no study on the self-cleaning effect of SiO 2 /WO 3 /ZnO films for solar cells. Experimental Materials and methods SiO 2 , WO 3 and ZnO solutions were prepared separately to prepare SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO films. To prepare the SiO 2 solution, tetraethylorthoxylsilicane (TEOS) (112 ml) was mixed with a certain amount of distilled water-anhydrous ethanol solution (36 ml-1090 ml). Then, concentrated hydrochloric acid solution (~ 0.2 ml, 36%) was added into the solution to obtain a final molar ratio of TEOS : ethyl alcohol : H 2 O : HCl as 1 : 37.5 : 4 : 0.004. The expected concentration of SiO 2 within the final solution was 3 wt%. The solution will be stirred in a closed glass vessel at the room temperature for 2 h. and held in the dark for 1 day [ 25 ]. To prepare the WO 3 solution, sodium tungstate dihydrate (Na 2 WO 4 ·2H 2 O) (3 g) was dissolved in 20 ml of distilled water and stirred at the room temperature. HCl solution (20 ml, 8 M) was added into the prepared solution. Then, the solution was stirred for 2 h at 80°C. After cooling to room temperature, the as-prepared solution was held in the dark for 1 day [ 26 ]. On the other hand, zinc acetate 2-hydrate (Zn(CH 3 COO) 2 ·2H 2 O) was used as a precursor of Zn atom to prepare the ZnO solution. Absolute ethanol and diethanolamine were used as a solvent and a solution stabilizer, respectively. In detail, 0.05 mol of Zn(CH 3 COO) 2 ·2H 2 O was dissolved in ethanol (100 ml) to obtain 0.5 M solution. The as-prepared solution was stirred for half an hour. Then, 0.05 mol of the solution stabilizer was added into the solution under stirring. Afterward, the solution was stirred for 30 min. The as-prepared solution was held in the dark for 1 day [ 27 ]. The SiO 2 solution and the WO 3 solution was mixed with varying ratios (80/20, 70/30, 60/40, 50/50, 40/60, 30/70 and 20/80 wt./wt.) to obtain the SiO 2 /WO 3 composite solutions. The composite solutions were stirred for 2 h and held in the dark for 1 day. Within the scope of the optimization study, the optimum SiO 2 /WO 3 composition was determined by using the photocatalytic activity measurements. The SiO 2 /WO 3 film composition, resulted the highest photocatalytic activity, was determined and the optimum SiO 2 /WO 3 composition was used in the remaining studies to prepare the SiO 2 /WO 3 /ZnO composites. In addition, the ZnO solution was mixed with varying ratios ((SiO 2 /WO 3 )/ZnO : 70/30, 80/20 and 90/10 wt./wt.) with the optimum SiO 2 /WO 3 solution to prepare the SiO 2 /WO 3 /ZnO composites. The composite films were labed as SiO 2 /WO 3 (x/y) based on the weight ratio of SiO 2 to WO 3 . In addition, the composite films were labed as SiO 2 /WO 3 /ZnO(x/y) based on the weight ratio of SiO 2 /WO 3 to ZnO. Ultrasonic cleaning was applied to the glass substrates prior to the dip-coating process. The as-prepared solutions were deposited on the glass substrates through the dip-coating technique at the ambient condition. After the dip-coating process, the glass substrate was dried at the ambient condition for 2 h. The as-deposited film was pre-heated at 100°C for 1 h to remove the unreacted volatile species. Afterward, it was annealed at 400°C for 2 h to provide the growth of the crystalline phase [ 25 ]. As a process parameter, the number of the dip-coating cycle was changed to investigate the effect of the film thickness on the photocatalytic activity, the light transmittance ratio and the efficiency loss of the solar cell. Structural, morphological and optical characterization Fourier transform infrared (FTIR) spectra of the film samples was be obtained by scanning between the wavenumber range of 4000 to 400 cm − 1 using a Bruker IFS 66/S model FTIR spectrophotometer with a resolution of 4 cm − 1 . It was planned to evaluate the chemical bond structures of the photocatalyst systems using the FTIR spectrocopy. X-ray diffraction (XRD) patterns of the film samples was recorded to identify the crystal structure. A Rigaku Ultima IV model X-ray diffractometer was used with monochromatic Cu Kα radiation (λ = 1.5406 Å) at a scan rate of 1°/min. The morphology of the coated films was examined with a QUANTA 400F fied emission scanning electron microscope (FESEM). A conductive coating was deposited on the samples prior to the analysis. The distribution and the interaction of the composite constituents within the composite structure was examined using the FESEM images. The elemental composition of the film samples was investigated by energy dispersive X-ray (EDX) spectroscopy (JXA-8230 EDX Microanalysis Instrument). The transmittance and absorbance spectrum of the coated films were recorded in the wavelength range of 200 nm to 800 nm using a Genesys 10S (Thermo Scientific) model spectrophotometer. The UV-Vis absorbance spectrum was used to determine the optical band gap of the coated film by using the Tauc equation given below [ 2 ]: αhʋ = A(hʋ - Eg) 1/2 (1) at which α, Eg and hʋ are the absorption coefficent, the optical band gap energy and the photon energy, respectively. The optical band gap energy was estimated by extrapolating the linear part of the curve to the x-axis on the plot of (αhν) 2 vs. hv. The film coatings should not reduce the efficiency of the solar cell due to a possible decrease in the solar light transmittance. The negative effects of self-cleaning coatings on the efficiency of the solar cell was also examined in the scope of this study. Most of the studies conducted on the self-cleaning coatings for the PV system have neglected to measure the efficiency loss that might occur in the solar cell. The efficiency of the self-cleaning coated solar cell and the uncoated solar cell was compared. The efficiency of a solar cell was calculated using the following equation: η (efficiency) = V OC I SC FF / P in (2) where V OC is the open-circuit voltage, I SC is the short-circuit voltage and FF is the fill factor. The glass substrate coated with the self-cleaning coating was placed on the top of a solar cell and the efficiency of this solar cell was measured. As a reference, an uncoated glass substrate was also placed on the top of the solar cell and the efficiency was measured. Characterization of the Cr(VI) photoreduction performance The photocatalytic activity of the as-prepared coatings, soiled with a model organic compound (methylene blue), was monitored under UVA light irradiation (12 W). For this purpose, the coated film samples were immersed into the methylene blue solution (10 mg/l) and then dried in the air atmosphere. The coatings adsorbed with methylene blue will be irradiated with UVA light and at certain time intervals (30 min.), the degradation of methylene blue on the coatings was evaluated by measuring the reduction in the absorbance maximum peak of the model compound (664 nm) using a Genesys 10S model (Thermo Scientific) spectrophotometer by the following equation [ 7 ]: Degradation efficiency (%) = (A 0 -A)/A 0 (3) where A 0 is the initial absorbance of methylene blue and A is the absorbance of methylene blue after the UV light irradiation. In addition, the photocatalytic activity of the optimum SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO films was analyzed using the water contact angle measurement. Photocatalytic degradation of a model dye, methyl stearate, on the coated surface has been reported in the literature by Ren et al. (2020). According to the method described, methylene blue was dissolved in distilled water (10 mg/l) and it was tried to be adsorbed on the coated films by the dip coating technique. The sample containing the organic pollutant was then exposed to the UVA light. The degradation of the organic pollutant was observed by measuring the water contact angle on the glass surface at certain time intervals (30 min). The contact angle measurement of the water drop was performed at 3 different points on the coating surface according to the fixed drop (sessile drop) method using an optical tensiometer (Theta Lite, Biolin Scientific) [ 28 ]. Results and discussion FTIR analysis As illustrated in Fig. 1 a, FTIR absorbance spectrum confirmed the successful synthesis of SiO 2 . There is a broad band on the FTIR spectrum of SiO 2 from 2800 cm − 1 to 3800 cm − 1 , assigned to the presence of the O-H group [ 29 ]. In addition, there is a weak absorbance peak at 1623 cm − 1 , assigned to the O-H stretching bond [ 29 ]. On the other hand, there are strong absorbance peaks at 453 cm − 1 , 819 cm − 1 and 1074 cm − 1 , attributed to the asymmetric and symmetric Si-O-Si stretching vibrations [ 29 , 30 ]. The weak absorbance peak at 1378 cm − 1 might be due to the C-H bond of the SiO 2 precursor (TEOS) [ 30 ]. On the FTIR spectrum of pure WO 3 film (Fig. 1 b), there is a broad absorbance band at around 590 cm − 1 and a sharp absorbance peak at around 800 cm − 1 , which were attributed to the W = O stretching bond and the O-W-O stretching bond, respectively [ 31 ]. FTIR spectrum of pure ZnO film illustrates characteristic peak of ZnO at 482 cm − 1 and 555 cm − 1 , which were attributed to the Zn-O stretching vibrations (Fig. 1 c) [ 32 ]. In addition, there are additional peaks at 865 cm − 1 , 1039 cm − 1 , 1392 cm-1 and 1629 cm-1, which were assigned to the symmetric bending of the H-O-H bond, the stretching vibration of the C-O bond of the primary alcohol, the secondary alcohol vibration and the vibration mode of alkyls, respectively [ 32 , 33 ]. Also, there is a wide absorbance band at around 3438 cm − 1 and peaks at 2896 cm − 1 , 2975 cm − 1 due to the to the stretching vibration of hydroxyl compounds [ 32 , 33 ]. In Fig. 1 d, FTIR absorbance spectrum of the composite film sample confirmed the successful synthesis of both SiO 2 and WO 3 together. The characteristic absorbance peaks of WO 3 were observed at 667 cm − 1 and 966 cm − 1 , assigned to the W = O stretching bond [ 31 ]. The spectrum also presents the characteristic peak of WO 3 at 957 cm − 1 , belonging to the stretching of short W = O bonds of WO 3 .H 2 O. On the other hand, the characteristic peaks of SiO 2 were observed at 467 cm − 1 , 797 cm-1 and 1083 cm − 1 , attributed to the Si-O-Si stretching vibrations [ 29 , 30 ]. In addition, there is a weak absorbance peak at 1629 cm − 1 , which was attributed to the Si-OH vibrations [ 30 ]. FTIR spectrum exhibits a broad band at around 3410 cm − 1 due to the O-H group [ 29 ]. On the FTIR spectrum of the SiO 2 /WO 3 /ZnO(70/30) (Fig. 1 e), the characteristic absorbance peak of SiO 2 due to the Si-O-Si stretching vibrations appears at 463 cm − 1 and 1067 cm − 1 , respectively [ 29 , 30 ]. The peak present at 515 cm − 1 might belong to the Zn-O stretching vibrations [ 32 ]. Characteristic peaks of WO 3 due to the W = O stretching bond and the O-W-O stretching bond are present at 620 cm − 1 and 806 cm − 1 , respectively, on the same spectrum [ 31 ]. On the spectrum, there are additional peaks at 871 cm − 1 , 1624 cm − 1 , 3445 cm − 1 and 3512 cm − 1 , which were attributed to the stretching vibration of hydroxyl compounds [ 29 , 32 , 33 ]. XRD analysis The XRD analysis was conducted to investigate the crystal structure of pure and composite film samples. Figure 2 a illustrates the XRD pattern of the SiO 2 film. The XRD profile of the SiO 2 film exhibited a broad peak at round 23° owing to the formation of amorphous SiO 2 nanoparticles [ 34 ]. According to Fig. 2 b, all the peaks on the XRD pattern, in well accordance with the JCPDS No. 83–0950, might be consigned to the monoclinic WO 3 crystal phase. The more intense peaks at 23.6°, 24.3°, 26.6°, 28.8°, 34.1°, 41.9°, 48.4°, 49.9° and 55.8° corresponding to the (002), (200), (120), (112), (202), (222), (040), (-114) and (142) planes provided a strong evidence for the monoclinic WO 3 phase [ 35 ]. Figure 2 c illustrates the XRD pattern of pure ZnO film. The peaks of the ZnO film belongs to the typical hexagonal wurtzite structure. The diffraction pattern exhibited sharp and intense peaks at 31.9°, 34.5°, 36.4°, 47.7°, 56.7°, 63.0° and 68.1° corresponding to the (100), (002), (101), (102), (110), (103) and (112) planes of the ZnO phase, respectively (JCPDS No. 36-1451) [ 36 ]. No impurity phase was observed for pure ZnO, revealing the successful synthesis of ZnO in the film structure. Figure 2 d shows the XRD pattern of the SiO 2 /WO 3 (30/70) film sample. The XRD pattern exhibited characteristic peaks of the WO 3 phase corresponding to the (002), (200), (120), (112), (202), (222), (040), (-114), (142) and (142) planes at the diffraction angle of 23.6°, 24.3°, 26.6°, 28.6°, 34.1°, 41.8°, 48.3°, 49.9°, 55.7° and 56.4°, respectively. The broad peak belonging to the amorphous SiO 2 structure could not be detected on the XRD pattern of the composite film. Within the composite structure, the amorphous SiO 2 phase might be converted to the crystalline phase. According to the standard card of the crystalline SiO 2 (JCPDS data of 46-1045), there are two characteristic peaks of SiO 2 at 21.1° and 26.6° [ 37 ]. The peak at 21.1° was not present on the XRD pattern of the composite film sample. The peak at 26.6° might be lost in the peak of WO 3 at 26.6°. When compared with pure WO 3 , there was a slight shift in the peak position toward the side of smaller diffraction angle with the composite film structure. Figure 2 e illustrates the XRD pattern of the SiO 2 /WO 3 /ZnO(70/30) film sample. The XRD pattern exhibited characteristic peaks of the WO 3 phase corresponding to the (002), (200), (120), (112), (222), (040), (-114) and (142) planes at 2θ values of 23.8°, 24.5°, 25.9°, 29.9°, 41.3°, 48.3°, 48.7° and 55.6°, respectively. The same pattern included characteristic peaks of the ZnO phase at 31.2°, 33.6°, 36.6°, 47.7°, 64.7° and 68.2°. The characteristic peak belonging to the crystalline SiO 2 phase was present at 21.1°, suggesting that the amorphous SiO 2 phase was converted to the crystalline phase. Morphological analysis Figure 3 shows the FESEM images of pure SiO 2 , pure WO 3 and pure ZnO film samples. Pure SiO 2 film is homogeneous and without cracks over a wide area. In addition, the SiO 2 film has a smooth surface area. On the other hand, there is no smooth surface area with the WO 3 and ZnO films. There was a significant grain growth on the WO 3 and ZnO film surfaces. The crystal grains were less tightly packed on both of the film surfaces. When compared with the WO 3 film surface, the surface of the ZnO film seems to be smoother. Figure 3 also shows the EDX spectrum of pure SiO 2 , pure WO 3 and pure ZnO film samples. The EDX spectroscopy proved the successful synthesis of SiO 2 , WO 3 and ZnO films from their precursor solutions. Figure 4 illustrates the FESEM images of the SiO 2 /WO 3 (30/70) film and the SiO 2 WO 3 /ZnO(70/30) film samples. The surface structure of the SiO 2 /WO 3 (30/70) film is similar to the surface structure of pure WO 3 film. There was also a significant grain growth on the composite film surface. The grain structure might belong to the WO 3 phase of the composite film. Compared to pure WO 3 film, the grain structures seem to be smaller. As the WO 3 phase was the dominant phase in the composite, smooth surface areas belonging to the SiO 2 phase were not obvious on the FESEM image of the SiO 2 /WO 3 (30/70) film sample. The SiO 2 phase might be embedded into the WO 3 phase, forming a homogeneous SiO 2 /WO 3 film layer. On the FESEM image of the SiO 2 /WO 3 /ZnO(70/30) film, there was also a significant grain growth. There are two different grain structures in two different sizes. The larger grain structures might belong to the ZnO phase and the smaller grain structure might belong to the WO 3 phase. Compared to the SiO 2 /WO 3 (30/70), the surface structure of the SiO 2 /WO 3 /ZnO(70/30) seems to be less smooth. EDX spectrum of the SiO 2 /WO 3 (30/70) film and the SiO 2 /WO 3 /ZnO/70/30) film samples exhibited all the elements of the composite constituents. According to the EDX spectra, both of the composite films were successfully prepared. Figure 5 illustrates the optical microscopy image of the film samples. In all images, there are very few cracks. The cracks, which could occur during the dip coating and drying processes due to the removal of solvent at high speeds, might disappear during the annealing process at 400°C. The dark spherical regions in the SiO 2 /WO 3 (30/70) film might belong to the WO 3 phase. The optical microscope images of pure SiO 2 and pure WO 3 films supported this idea. Pure SiO 2 film includes only crack and there are no dark spherical regions. On the other hand, pure WO 3 film includes only a large dark region. According to the optical microscope images, smooth and homogeneous film surfaces were obtained. The optical microscope image of the SiO 2 /WO 3 /ZnO film is similar to the image of the SiO 2 /WO 3 film. As a difference, there are more dark regions in different sizes. Small-sized and large-sized regions might belong to the WO 3 and ZnO phases, respectively. Light transmittance study Figure 6 shows the light transmitance spectrum of the film samples. Pure WO 3 film exhibited low transmittance of about 44% between 300–800 nm, whereas pure SiO 2 film exhibited high transmittance (~ 92%) in the same region. Hence, an increase in the WO 3 content of the composite film resulted in a reduction in the average transmittance in the whole visible region (Fig. 6 d- 6 j). According to Fig. 6 d, uncoated glass slide transmitted more UVA light between 320–470 nm than the glass slide coated with the SiO 2 /WO 3 (80/20) film. The transparency of the SiO 2 /WO 3 (80/20) film in the visible light spectrum (above 470 nm) was almost 3% higher than that of uncoated glass slide. The reason for the enhancement in the transparency might be the reduced reflectance on the SiO 2 /WO 3 (80/20) film. Figure 6 e and 6 f exhibits the transmittance spectra of the SiO 2 /WO 3 (70/30) and SiO 2 /WO 3 (60/40) film samples. The average transmittance of the SiO 2 /WO 3 (70/30) and SiO 2 /WO 3 (60/40) film samples in the visible light range was almost 85% and 86%, respectively. As compared to uncoated glass slide (91%), the SiO 2 /WO 3 (70/30) and SiO 2 /WO 3 (60/40) film samples exhibited lower transmittance. The average light transmittance of the SiO 2 /WO 3 (50/50) film in the visible region was around 91%, which was almost the same light transmittance as the uncoated glass slide. The remaining film samples (SiO 2 /WO 3 (40/60), SiO 2 /WO 3 (30/70) and SiO 2 /WO 3 (20/80)) showed average transmittance between 77% and 70% in the visible light region (Fig. 6 h- 6 j). The SiO 2 /WO 3 (30/70) composite film was also combined with ZnO during the dip coating process. Pure ZnO film exhibited nearly high light transmittance (~ 88%) in the visible light range as the uncoated glass slide. Hence, it was expected that the contribution of the ZnO phase into the SiO 2 /WO 3 composite structure might enhance the light transparency. As expected SiO 2 /WO 3 /ZnO film systems provided higher transmittance than that of the SiO 2 /WO 3 (30/70) film sample (Fig. 6 k). The SiO 2 /WO 3 /ZnO(90/10) has an average transmittance of 83% in the visible light region. The transmittance of the SiO 2 /WO 3 /ZnO film samples increased with the ZnO content. The SiO 2 /WO 3 /ZnO(80/20) and SiO 2 /WO 3 /ZnO(70/30) film samples achieved average transmittance of 85% and 87%, respectively (Fig. 6 l and 6 m). Within the scope of the optimization study, the number of the dip-coating cycle was changed to investigate the effect of the film thickness on the light transparency. Fig. S1 exhibits the transmittance spectra of the SiO 2 /WO 3 (70/30) film sample. The average transmittance of the SiO 2 /WO 3 (70/30) (1-fold coating), SiO 2 /WO 3 (70/30) (2-fold coating) and SiO 2 /WO 3 (70/30) (3-fold coating) film samples in the visible light range was almost 72%, 65% and 57%, respectively. In addition, the average transmittance of the SiO 2 /WO 3 /ZnO(70/30) (1-fold coating), SiO 2 /WO 3 /ZnO(70/30) (2-fold coating) and SiO 2 /WO 3 /ZnO(70/30) (3-fold coating) film samples in the visible light range was almost 87%, 72% and 63%, respectively. When the number of the dip-coating cycle increased, the light transparency decreased for the film samples. With an increase in the numbe of the dip-coating cycle, the film thickness might increase or the film might turn into a denser structure. UV-Vis Spectrocopy As shown in Fig. 7 , the SiO 2 /WO 3 (80/20) film sample exhibited absorption in the UVA light region (315–400 nm). When the WO 3 content of the film sample increased, the absorption band widened to the visible light region and the optical absorption of the composite film samples in the UVA light region was significantly improved. Pure WO 3 film exhibited absorption in both UV and visible light regions, while pure SiO 2 film exhibited low absorption only in the UV range (~ 300 nm). As expected WO 3 contribution improved the optical absorption ability of the composite film. It would be appropriate to extend the photocatalytic reaction application to the visible light region. But, it can be detrimental to the solar cell in terms of the efficiency. The photovoltaic market is mainly based on crystalline silicon, which can absorb almost one-third of usable solar photons. Photons in the red and near-infrared portion of the sun light spectrum (700–1100 nm) can be absorbed by the silicon. Photons with longer wavelengths cannot be absorbed by the silicon. On the other hand, photons with shorter wavelengths can be absorbed by the silicon and they have more energy than the silicon needs, causing the excess energy to be released as heat [ 38 ]. As specified before WO 3 widened the edge of the absorption band to the visible light, which might lead to a decrease in the intensity of the sun light reaching to the absorber layer of the solar cell. Any decrease in the number of photons in the visible light region (400–700 nm) might affect the solar cell efficiency. As estimated from the Tauc plot (Fig S2), the optical band gap energy of pure SiO 2 and WO 3 films were estimated to be 4.80 eV and 2.35 eV, respectively. According to Fig. S3, the optical band gap energy was calculated to be 2.95 eV, 2.80 eV, 2.15 eV, 2.35 eV, 2.45 eV, 2.00 eV and 2.25 eV for SiO 2 /WO 3 (80/20), SiO 2 /WO 3 (70/30), SiO 2 /WO 3 (60/40), SiO 2 /WO 3 (50/50), SiO 2 /WO 3 (40/60), SiO 2 /WO 3 (30/70), SiO 2 /WO 3 (20/80), respectively. It was expected that the optical band gap energy would decrease as the WO 3 content of the composite film sample increased. The optical band gap energy of the composite film samples ranged from 2.00 eV to 2.95 eV. The UV-Vis absorption spectrum of the SiO 2 /WO 3 /ZnO film samples is also shown in Fig. 7 . The SiO 2 /WO 3 /ZnO(90/10) film sample has a weak absorption in the UV region (in the range of 250–400 nm). The intensity of the absorption band increased as the ZnO content of the film sample increased. Since the solar cell generates electricity by absorbing mostly the visible light region of the incoming sunlight, absorption in the UV light range was not expected to have a negative impact on the efficiency of the solar cell. According to the Tauc plot analysis (Fig. S4), the optical band gap energy was estimated to be 2.70 eV, 2.95 eV and 3.20 eV for the SiO 2 /WO 3 /ZnO(90/10), SiO 2 /WO 3 /ZnO(80/20) and SiO 2 /WO 3 /ZnO(70/30) film samples, respectively. The optical band gap of the SiO 2 /WO 3 /ZnO film sample was widened with an increase in the ZnO content, which might be detrimental to the photocatalytic activity and beneficial to the solar cell efficiency. Photocatalytic dye degradation efficiency WO 3 has been widely studied as a photocatalyst due to its superior properties such as photostability, non-toxicity, chemical and thermal stability. In addition, it exhibits excellent solar radiation absorption due to its favorable band gap [ 39 ]. However, there is a main problem, limiting the pratical application of WO 3 . The rapid recombination of the photoexcited electrons with holes leads to a low quantum efficiency and photocatalytic dye degradation efficiency. In literature, many attempts have been performed to reduce the recombination rate of the photoinduced charge carriers on the photocatalyts. Coupling WO 3 with another semiconductor can reduce the recombination rate of the mobile charge carriers [ 39 , 40 ]. Within the scope of the coupling WO 3 with another semiconductor, WO 3 was combined with SiO 2 in the composite film structure. The photocatalytic degradation of methylene blue might be composed of four steps. When the film sample was exposed to UV light, the valence band electrons were excited to the conduction band to form photoexcited electron-hole pairs (4). The photoinduced charge carriers transferred to the surface of the film sample and reacted with the dye molecules. The surface adsorbed H 2 O molecules might be oxidized by the photogenerated holes to hydroxyl radicals (5) and the dissolved O 2 molecules might be reduced by the photogenerated electrons to superoxide radicals on the surface of the film samples (6). Both of these radicals are highly active and can degrade any organic molecules into simple molecules like H 2 O and CO 2 (7) [ 41 ]. SiO 2 /WO 3 + hv → e − + h + (4) H 2 O + h + → ·OH + H + (5) O 2 + e − → ·O 2 − (6) ·O 2 − + ·OH + organic dye → degradation products (7) Figure S5 and S6 illustrate UV-Vis absorption spectra of methylene blue in the presence of pure and the SiO 2 /WO 3 composite film samples. The absorption intensity decreased gradually with time under the UVA light irradiation for all film samples. At the end of 240 min of UVA light irradiation, the maximum absorption peak of methylene blue decreased to the lowest value with the SiO 2 /WO 3 (30/70) sample, which means that the highest photocatalytic dye degradation was obtained with the specified film sample. The photocatalytic dye degradation efficiency of the as-prepared film samples was calculated using the initial absorbance of the dye solution and the absorbance value of methylene blue solution exposed to the UVA light irradiation. In order to better compare the photocatalytic activity of the SiO 2 /WO 3 composite films, all dye degradation efficiency values were plotted in Fig. 8 . After 240 min of the UVA light irradiation, the photocatalytic dye degradation efficiency was 25.2%, 46.1%, 53.5%, 68.8%, 75.2%, 84.6%, and 58.2% for the SiO 2 /WO 3 (80/20), SiO 2 /WO 3 (70/30), SiO 2 /WO 3 (60/40), SiO 2 /WO 3 (50/50), SiO 2 /WO 3 (40/60), SiO 2 /WO 3 (30/70) and SiO 2 /WO 3 (20/80) films, respectively. The SiO 2 /WO 3 (30/70) film sample exhibited the highest photocatalytic activity. When compared with pure SiO 2 and pure WO 3 film samples, there was a significant enhancement in the photocatalytic activity of the composite film samples (Fig. 8 ). Pure SiO 2 and pure WO 3 film samples were able to degrade 5.6% and 24.0% of methylene blue, respectively, after 240 minutes of the UVA light irradiation. According to Hu and his coworkers (2012), the interaction between SiO 2 and WO 3 in the composite structure might led to the formation of the oxygen vacancy. The oxygen vacancy led to the formation of a defect state between the conduction and valence bands of WO 3 . The specified defect state might act as the hole trap, suppressing the recombination rate of the photogenerated electron-hole pairs [ 42 ]. Any effect that decreases the recombination rate of the photoinduced electron-hole pairs or increases the number of charge carriers positively affects the photocatalytic efficiency. In literature, according to Li and his coworkers (2014), the SiO 2 surface was rich in the hydroxyl radicals in the aqueous medium. The increase in the number of the hydroxyl radicals on the SiO 2 surface improved the ability of the composite sample to retain the absorbed water, which might result in an increase in the reaction rate between the dye molecules and WO 3 . In addition, SiO 2 had a high tendency to trap the photoexcited electrons in its conduction band, suppressing the recombination rate of the photogenerated electron-hole pairs [ 19 ]. The electron trapping ability of SiO 2 might also be the reason for the significant enhancement in the photoactivity of the SiO 2 /WO 3 composite film sample. The trapping of the photoexcited electrons of WO 3 on the conduction band of SiO 2 might contribute to the effective separation of the mobile charge carrier, which are necessary to form the active radicals responsible for the degradation of the organic dye molecules. The weight ratio of SiO 2 to WO 3 was critical in terms of the photocatalytic activity. The weight ratio of the composite constituents might affect the contact effectiveness between SiO 2 and WO 3 particles. The excess of any of the composite components might reduce the contact between the SiO 2 and WO 3 particles. According to Fig. 8 , the optimum composition (SiO 2 /WO 3 (30/70)) might provide the effective contact between SiO 2 and WO 3 particles. Increasing or decreasing the WO 3 content of the composite from the optimum value might reduce the contact interface between SiO 2 and WO 3 particles, suppressing the effective transfer of the photoinduced electron-hole pairs between the composite constituents. Hence, many photoinduced charge carriers might recombine on SiO 2 and WO 3 , decreasing the photocatalytic dye degradation efficiency [ 43 ]. According to Jourshabani and Lee (2021), the bottom energy state of the conduction band for WO 3 and SiO 2 were equivalent to -0.66 eV and − 0.56 eV (vs NHE), respectively. The top energy state of the valence band for WO 3 and SiO 2 were equivalent to 2.26 eV and 3.65 eV (vs NHE), respectively. Coupling WO 3 and SiO 2 in the composite structure affected the charge transfer by different pathways, leading to an improvement in the photocatalytic activity [ 43 ]. The contact points between SiO 2 and WO 3 might have a significant role in suppressing the recombination of the photoexcited electron-hole pairs, which was also confirmed by Jourshabani and Lee (2021) [ 43 ]. The SiO 2 /WO 3 composite could form hydroxyl radicals from surface adsorbed water molecules because the composite could provide sufficient driving force for the formation of the oxidation reaction of OH − /•OH (1.99 eV vs. NHE). In addition, the composite sample could form superoxide radicals from surface adsorbed oxygen molecules because the conduction band position of both WO 3 and SiO 2 could overcome the thermodynamic barrier of the reduction reaction of O 2 /•O 2 − (-0.33 eV vs NHE) [ 43 ]. Because of the potential differences in the band energy levels of SiO 2 and WO 3 , the photoexcited electrons of WO 3 could transfer to the conduction band SiO 2 (Fig. 9 ). The opposite was true for the photoexcited holes formed on SiO 2 . The photogenerated holes of SiO 2 could transfer to the valence band of WO 3 . Thus, the photoinduced electron-hole pairs might be effectively separated. The superoxide radicals might be generated directly or indirectly by the photoinduced electrons of SiO 2 and WO 3 . Similarly, the hydroxyl radicals might be formed directly or indirectly by the photoinduced holes of WO 3 and SiO 2 [ 43 ]. The Langmuir-Hinshelwood model was utilized to analyze the reaction rate of heterogeneous photocatalysis for the degradation of methylene blue on the film samples. The Langmuir-Hinshelwood model formula is given below [ 44 ]: ln(C 0 /C) = kt (8) where C 0 and C are the concentration of methylene blue solution before and after the UV light irradiation, respectively. In addition, k is the apparent pseudo-first-order reaction rate constant, which was obtained from the plot of ln(C/C 0 ) vs. t (Fig. S7). Fig. S7 confirmed that the pseudo-first-order was followed by the photocatalytic dye degradation reactions in the presence of the SiO 2 /WO 3 film samples. The reaction rate constant values were compared on Table 2 . The highest reaction rate constant was obtained with the SiO 2 /WO 3 (30/70) film sample. Compared to pure SiO 2 and WO 3 film samples, a significant increase in the reaction rate of the photocatalytic degradation of methylene blue was obtained with the SiO 2 /WO 3 (30/70) film sample (Table 3 ). Table 2 The photocatalytic dye degradation rate on the SiO 2 /WO 3 film samples Sample k (min − 1 ) R 2 SiO 2 /WO 3 (80/20) 0.0015 0.7897 SiO 2 /WO 3 (70/30) 0.0027 0.9913 SiO 2 /WO 3 (60/40) 0.0036 0.9088 SiO 2 /WO 3 (50/50) 0.0059 0.7879 SiO 2 /WO 3 (40/60) 0.0065 0.9369 SiO 2 /WO 3 (30/70) 0.0078 0.9905 SiO 2 /WO 3 (20/80) 0.0038 0.9970 Table 3 The photocatalytic dye degradation rate on pure SiO 2 , pure WO 3 and ZnO film samples Sample k (min − 1 ) R 2 Pure SiO 2 0.0002 0.9705 Pure WO 3 0.0012 0.9833 Pure ZnO 0.0163 0.2326 To enhance the photocatalytic dye degradation efficiency of the SiO 2 /WO 3 composite system, it was also coupled with a well-known photocatalyst ZnO. Since the highest photocatalytic activity was obtained with the SiO 2 /WO 3 (30/70) film sample, this composition was utilized to prepare the SiO 2 /WO 3 /ZnO composite films. Fig. S8 shows the absorption spectrum methylene blue in the presence of SiO 2 /WO 3 /ZnO film samples. A decrease in the absorption spectrum intensity was observed with time under the UVA light irradiation. Figure 10 illustrates the percentage of the photocatalytic degradation of the model dye in the aqueous solution using the SiO 2 /WO 3 /ZnO film samples. Compared to the optimum SiO 2 /WO 3 composite film sample (SiO 2 /WO 3 (30/70)), the photocatalytic degradation percentage of methylene blue was enhanced on the SiO 2 /WO 3 /ZnO film sample. Combining the optimum SiO 2 /WO 3 composition with ZnO seemed to be effective in terms of the photocatalytic activity. The maximum dye degradation percentage for SiO 2 /WO 3 /ZnO(90/10), SiO 2 /WO 3 /ZnO(80/20) and SiO 2 /WO 3 /ZnO(70/30) was obtained as 86.1%, 86.3% and 91.6%, respectively (Fig. 10 ). Figure S9 illustrates the kinetics of the photocatalytic degradation of the model dye. The degradation kinetics seemed to fit to the pseudo-first-order reaction model (Table 4 ). The reaction rate constant value for SiO 2 /WO 3 /ZnO(90/10), SiO 2 /WO 3 /ZnO(80/20) and SiO 2 /WO 3 /ZnO(70/30) were 0.0088, 0.0088 and 0.0110 min − 1 , respectively. The reaction rate constant values revealed that the SiO 2 /WO 3 /ZnO composites were more active to degrade the dye molecules in the aquatic environment under the UVA irradiation. With the contribution of ZnO to the SiO 2 /WO 3 composite system, the reaction rate was increased by about 1.4 times. Due to its high photocatalytic activity, ZnO might enhance the photocatalytic dye degradation efficiency of the resulting composite system. Table 4 Reaction rate constant values of the model dye degradation on the SiO 2 /WO 3 /ZnO films under the UVA light irradiation Sample k (min − 1 ) R 2 SiO 2 /WO 3 /ZnO(70/30) 0.0110 0.9705 SiO 2 /WO 3 /ZnO(80/20) 0.0088 0.9939 SiO 2 /WO 3 /ZnO(90/10) 0.0088 0.9914 According to Lu and his coworkers (2016), the bottom energy state of the conduction band for ZnO was equivalent to -0.26 eV (vs NHE) and the top energy state of the valence band for ZnO was equivalent to 2.85 eV (vs NHE) [ 45 ]. When ZnO was combined with SiO 2 /WO 3 , the conduction band potential of ZnO was more positive than that of SiO 2 and WO 3 (Fig. 9 ). In addition, the valence band potential of ZnO was more positive than that of WO 3 . Thus, the photoinduced electrons of both WO 3 and SiO 2 might transfer to the conduction band of ZnO. Also, the photoinduced holes of ZnO might transfer to the valence band of WO 3 . Hence, the SiO 2 /WO 3 /ZnO heterostructure might effectively separate the photogenerated mobile charge carriers on the SiO 2 /WO 3 composite, further improving the photocatalytic dye degradation efficiency. The effectively separated electron-hole pairs could migrate to the photocatalyst surface to form the active radicals necessary to degrade the methylene blue molecules. ZnO in the composite structure could also form the hydroxyl radical from the surface adsorbed water molecules because the redox potential of the couple OH − /•OH, which is 1.99 eV vs. NHE, was more negative than the valence band edge potential of ZnO. According to the redox potentials of the couple O 2 /·O 2 − (-0.33 eV vs. NHE), the surface adsorbed O 2 molecules could not be reduced by the photogenerated electrons of ZnO to superoxide anion radicals (·O 2 − ) [ 43 ]. Within the scope of the optimization study, the effect of the number of the dip-coating cycle on the photocatalytic activity was also studied. According Fig. 11 , SiO 2 /WO 3 (30/70) (1-fold coating), SiO 2 /WO 3 (30/70) (2-fold coating), SiO 2 /WO 3 (30/70) (3-fold coating) film samples exhibited the dye degradation efficiency of 84.6%, 86.6% and 81.1%, respectively, after 240 min. Figure 11 also illustrates the photocatalytic degradation of the model dye on SiO 2 /WO 3 /ZnO(70/30) (1-fold coating), SiO 2 /WO 3 /ZnO(70/30) (2-fold coating) and SiO 2 /WO 3 /ZnO(70/30) (3-fold coating) film samples, respectively. When the model dye was irradiated on the 1-fold coated SiO 2 /WO 3 /ZnO(70/30), 2-fold coated SiO 2 /WO 3 /ZnO(70/30) and 3-fold coated SiO 2 /WO 3 /ZnO(70/30) films samples, the degradation of methylene blue reached the maximum of 91.6%, 91.0% and 90.0%, respectively, after 240 min of the UVA light irradiation. It was observed that the degradation of the model dye was weakly dependent on the number of the dip-coating cycle. Solar Cell Efficiency Glass slides coated with the SiO 2 /WO 3 or SiO 2 /WO 3 /ZnO film samples were used to measure the effect of the coated film on the real solar cell. Figure 12 illustrates the variation of the obtained voltage with the current by an uncoated and coated solar cells. The fill factor (FF) and the efficiency of the uncoated (standard) solar cell and coated solar cells were summarized on Table 5 . In general, relatively higher solar cell efficiency was achieved with the composite films including high SiO 2 content. The solar cell efficiency experiment was performed under a solar light simulator. Due to its wide optical band gap, the SiO 2 film could transmit most of the incident light to the absorber layer of the solar cell. The WO 3 film coating, which has a narrower optical band gap than that of SiO 2 , could reduce the efficiency of the solar cell by absorbing more of the incoming light. The light transmittance spectroscopy supported this idea. The composite film samples with high SiO 2 content exhibited high transmittance in both UV and visible light regions. Compared to the uncoated solar cell (standard), higher efficiency was achieved by the solar cell including the SiO 2 /WO 3 (70/30) and SiO 2 /WO 3 (50/50) film samples, respectively. The reason for the improvement in the solar cell efficiency might be the reflective feature of the specified film coatings. Figure 12 also illustrates the voltage-current characteristics of the solar cell coated with the SiO 2 /WO 3 /ZnO film samples. To prepare the SiO 2 /WO 3 /ZnO film samples, the SiO 2 /WO 3 (30/70) film sample was utilized and coupled with ZnO in varying compositions. Compared to the SiO 2 /WO 3 (30/70) film coating, the solar cell efficiency slightly increased. The wide optical band gap and the anti-reflective feature of ZnO might be the possible reason for the improvement in the solar cell efficiency. When compared with the uncoated solar cell (standard), approximately the same efficiency value was obtained with the solar cell coated with the SiO 2 /WO 3 /ZnO(90/10) and SiO 2 /WO 3 /ZnO(80/20) films, respectively. As the ZnO content of the SiO 2 -WO 3 /ZnO films increased, the solar cell efficiency slightly decreased. To analyze the individual effect of the composite phases on the solar cell efficiency, the voltage-current characteristics of the solar cell coated with pure SiO 2 , pure WO 3 and pure ZnO films were also analyzed and their results were shown in Fig. 12 . When compared with the standard solar cell, slightly higher and slightly lower efficiencies were achieved by the solar cell coated with pure SiO 2 film and pure ZnO film, respectively. On the other hand, pure WO 3 film significantly reduced the efficiency of the standard cell (from 5.51 to 2.69). Fill factor (FF) is one of the important parameters to determine the efficiency of a solar system. To get the maximum possible efficiency from a solar module, FF should be maximum and its value should approach one [ 46 ]. The fill factor, the ratio of the theoretical power to the maximum power, can be calculated by using the following relation (9): FF = V MP I MP / V OC I SC (9) where V OC is the open circuit voltage, I SC is the short circuit current, V MP is the voltage value at the maximum power point and I MP is the current at the maximum power point [ 46 ]. The fill factor is known as a measure of the quality of a solar cell. Among the solar cells coated with the SiO 2 /WO 3 films, only the solar cell coated with the SiO 2 /WO 3 (20/80) film had a slightly lower FF value than the standard solar cell. Among the solar cells coated with the SiO 2 /WO 3 /ZnO films, only the solar cell coated with the SiO 2 /WO 3 /ZnO(70/30) film exhibited a slightly lower FF value compared to the standard solar cell (Table 5 ). The calculated FF values showed that the prepared film samples could be applied to the cover glass of the real photovoltaic system. Within the scope of the optimization study, the effect of the number of the dip coating cycle on the solar cell efficiency was also studied (Fig. S10). According to Table 6 , as the number of the dip-coating cycle increased, the efficiency of the solar cell coated with SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO films slightly decreased. Maintaining or, if possible, increasing the efficiency of the solar cell is important for the applicability of the self-cleaning film layer on the solar cell. Therefore, increasing the number of the dip-coating cycle was useless in terms of the efficiency of the solar cell. Table 5 Efficiency of the uncoated (standard) and coated solar cells Sample V m (V) I m (A) V oc I sc F.F A (m 2 ) P out (W/m 2 ) P in (W/m 2 ) ɳ (%) Standard 0.30 0.147 0.475 0.224 0.415 0.0008 55.13 1000 5.51 SiO 2 0.315 0.144 0.473 0.217 0.442 0.0008 56.70 1000 5.67 ZnO 0.315 0.132 0.471 0.204 0.433 0.0008 51.98 1000 5.20 WO 3 0.207 0.104 0.299 0.152 0.474 0.0008 26.91 1000 2.69 SiO 2 /WO 3 (80/20) 0.289 0.150 0.434 0.227 0,440 0.0008 54.19 1000 5.42 SiO 2 /WO 3 (70/30) 0.306 0.147 0.442 0.214 0.476 0.0008 56.23 1000 5.62 SiO 2 /WO 3 (60/40) 0,307 0,140 0.461 0.211 0.442 0.0008 53.73 1000 5.37 SiO 2 /WO 3 (50/50) 0.292 0.161 0.421 0.235 0.475 0.0008 58.77 1000 5.88 SiO 2 /WO 3 (40/60) 0.261 0.128 0.413 0.195 0.415 0.0008 41.76 1000 4.18 SiO 2 /WO 3 (30/70) 0.266 0.119 0.385 0.175 0.469 0.0008 39.57 1000 3.96 SiO 2 /WO 3 (20/80) 0.264 0.129 0.419 0.197 0.413 0.0008 42.57 1000 4.26 SiO 2 /WO 3 /ZnO(90/10) 0.302 0.145 0.454 0.218 0.442 0.0008 54.74 1000 5.47 SiO 2 /WO 3 /ZnO(80/20) 0.309 0.142 0.437 0.207 0.485 0.0008 54.85 1000 5.48 SiO 2 /WO 3 /ZnO(70/30) 0.290 0.142 0.459 0.217 0.413 0.0008 51.48 1000 5.15 Table 6 Effect of the number of the dip-coating cycle on the efficiency of the solar cell coated with SiO 2 /WO 3 (30/70) and SiO 2 /WO 3 /ZnO(70/30) films Sample V MP (V) I MP (A) V oc I sc F.F A (m 2 ) P out (W/m 2 ) P in (W/m 2 ) ɳ (%) Standard 0.30 0.147 0.475 0.224 0.415 0.0008 55.13 1000 5.51 SiO 2 /WO 3 (30/70) 1-fold 0.266 0.119 0.385 0.175 0.469 0.0008 39.57 1000 3.96 SiO 2 /WO 3 (30/70) 2-fold 0.246 0.108 0.370 0.167 0.429 0.0008 33.21 1000 3.32 SiO 2 /WO 3 (30/70) 3-fold 0.198 0.097 0.316 0.148 0.411 0.0008 24.01 1000 2.04 SiO 2− WO 3 /ZnO(70/30) 1-fold 0.290 0.142 0.459 0.217 0.413 0.0008 51.48 1000 5.15 SiO 2− WO 3 /ZnO(70/30) 2-fold 0.262 0.119 0.393 0.180 0.441 0.0008 38.97 1000 3.90 SiO 2− WO 3 /ZnO(70/30) 3-fold 0.250 0.124 0.361 0.180 0.477 0.0008 38.75 1000 3.88 Water angle measurements One of the most conventional techniques to investigate the photocatalytic self-cleaning feature of the film samples is the dye technique [ 2 ]. In the dye technique, the model dye is considered as contamination on the film and the photocatalytic degradation of the dye molecules under the UV light radiation is studied to reveal the self-cleaning feature of the film coatings [ 2 ]. According to the photocatalytic dye degradation experiments, the prepared film samples could degrade the model dye adsorbed on itself under the UVA light irradiation. Hence, methylene blue as the model dye could be decomposed to water and carbon dioxide. The photocatalytic degradation rate of the methylene blue could be measured by analyzing the rate of water formation through the contact angle measurement [ 2 ]. The formation of water molecules on the film surface could change the surface energy, leading to a reduction in the water contact angle. The photocatalytic activity of the film samples was also studied using the dye technique. The water contact angle measurement was performed on the film samples adsorbed by the methylene blue and exposed the UVA light irradiation. Figure 13 illustrate the change of the water contact angle with the irradiation time, and Fig. S11 and S12 illustrate the images of the water droplets on the film samples. According to Fig. 13 , the water contact angle exhibited a decrease with the irradiation time. The water contact angle of the SiO 2 /WO 3 (30/70) film and the SiO 2 /WO 3 /ZnO(70/30) film decreased from 45.1°, 64.1° to 29.2°, 45.4°, respectively, after 240 min of the UVA light irradiation. The water contact angle measurement revealed that the composite film samples were able to degrade the model dye adsorbed on itself with time and the film samples exhibited photocatalytic activity. Both the photocatalytic dye degradation and the water contact angle measurements verified the high photocatalytic activity of the SiO 2 /WO 3 (30/70) and SiO 2 /WO 3 /ZnO(70/30) films. Conclusion The objective of this study was to coat the top layer of the solar cell with composite (SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO) films, which had the ability of self-cleaning under the UVA light irradiation. The film coatings provided the self-cleaning process through the photocatalytic activity and the photoinduced hydrophilicity. Within this scope, WO 3 was compounded with a highly transparent semiconductor SiO 2 , minimizing the the transmission loss on the solar cell. ZnO was also added into the film structure to provide an enhanced photocatalytic activity. The SiO 2 /WO 3 /ZnO film coatings exhibited high visible light transmittance and photocatalytic activity under the UVA light irradiation. The self-cleaning performance of the prepared film coatings was also so high that the SiO 2 /WO 3 /ZnO film could degrade more than 90% of the model contaminant on itself within 240 min of the UVA light irradiation. The hydrophilicty of the SiO 2 /WO 3 and SiO 2 /WO 3 /ZnO film coated with the model contaminant increased with the irradiation, exhibiting the photocatalytic degaradtion efficiency of the prepared films. The current-voltage measurement of the solar cell coated with the SiO 2 /WO 3 /ZnO film did not exhibit any significant loss in efficiency. The results of the study revealed that the SiO 2 /WO 3 /ZnO film can be applied as a comercial product on the PV panel surfaces against the accumulation of any kinds of pollution, resulting in the reduction of the PV efficiency. Declarations Author informations Ankara University, Engineering Faculty, Energy Systems Engineering, Ankara, 06830, TURKEY Ozcan Koysuren, Savas Yaglikci, Bilge Tuncel Polytechnic University of Tirana, Faculty of Mechanical Engineering, Department of Production and Management, Tirana, 1001, ALBANIA Klodian Dhoska, Irida Markja, Kirsehir Ahi Evran University, Faculty of Engineering and Architecture, Department of Environmental Engineering, Kirsehir, 40100, TURKEY Hafize Nagehan Koysuren Polytechnic University of Tirana, Faculty of Mechanical Engineering, Energy Department, Tirana, 1001, ALBANIA Elena Bebi Corresponding Author Correspondence to Ozcan Koysuren or Klodian Dhoska Statements & Declarations Funding This research has been supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK) and National Agency of Scientific Research and Innovation (NASRI) with the Project Number 122N383. Competing interests The authors have no relevant financial or non-financial interests to disclose. Author contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by all authors. Conflict of interest The authors declare no competing interests. References Estekhraji SAZ, Amiri S (2017) Sol-gel preparation and characterization of antibacterial and self-cleaning hybrid nanocomposite coatings. J Coat Technol Res 14(6):1335–1343 Khorshidi ZG, Jallab M, Moghbelli E, Goudarzi A, Ghaffari M (2021) Photocatalytic Analysis of a Hydrophilic Acrylic Coating/Zinc Oxide Nanocomposite on Glass Substrate. Polym-Plast Technol Mater 60(11):1220–1232 Pakdel E, Zhao H, Wang JF, Tang B, Varley RJ, Wang XG (2021) Superhydrophobic and photocatalytic self-cleaning cotton fabric using flower-like N-doped TiO2/PDMS coating. Cellulose 28(13):8807–8820 Watte J, Van Zele M, De Buysser K, Van Driessche I (2018) Recent Advances in Low-Temperature Deposition Methods of Transparent, Photocatalytic TiO2 Coatings on Polymers. Coatings 8(4):131 Gao Q, Wu XM, Cai LG (2021) Facial synthesis of K0.3WO3/Ag nanocomposites for self-cleaning energy efficient window coatings. J Alloys Compd 856:157069 Luevano-Hipolito E, Torres-Martinez LM, Cantu-Castro LVF (2019) Self-cleaning coatings based on fly ash and bismuth-photocatalysts: Bi2O3, Bi2O2CO3, BiOI, BiVO4, BiPO4. Constr Build Mater 220:206–213 Vulic T, Rudic O, Vucetic S, Lazar D, Ranogajec J (2015) Photocatalytic activity and stability of TiO2/ZnAl layered double hydroxide based coatings on mortar substrates. Cem Concr Compos 58:50–58 Noh HN, Myong SY (2014) Antireflective coating using a WO3-TiO2 nanoparticle photocatalytic composition for high efficiency thin-film Si photovoltaic modules. Sol Energy Mater Sol Cells 121:108–113 Soklic A, Tasbihi M, Kete M, Stangar UL (2015) Deposition and possible influence of a self-cleaning thin TiO2/SiO2 film on a photovoltaic module efficiency. Catal Today 252:54–60 Hosseini MS, Ebratkhahan M, Shayegan Z, Niaei A, Salari D, Rostami A, Raeisipour J (2020) Investigation of the effective operational parameters of self-cleaning glass surface coating to improve methylene blue removal efficiency; application in solar cells. Sol Energy 207:398–408 Jovanov V, Zecevic V, Vulic T, Ranogajec J, Fidanchevska E (2018) Preparation and characterization of protective self-cleaning TiO2/kaolin composite coating. Mater Constr 68(331):163 Rudakova AV, Emeline AV (2021) Photoinduced Hydrophilicity of Surfaces of Thin Films. Colloid J 83(1):20–48 Syafiq A, Pandey AK, Adzman NN, Abd Rahim N (2018) Advances in approaches and methods for self-cleaning of solar photovoltaic panels. Sol Energy 162:597–619 Thwala MM, Dlamini LN (2020) Photocatalytic reduction of Cr(VI) using Mg-doped WO3 nanoparticles. Environ Technol 41(17):2277–2292 Nagarjuna R, Challagulla S, Sahu P, Roy S, Ganesan R (2017) Polymerizable sol-gel synthesis of nano-crystalline WO3 and its photocatalytic Cr(VI) reduction under visible light. Adv Powder Technol 28(12):3265–3273 Ai L, Jia D, Guo N, Xu M, Zhang S, Wang L, Jia L (2020) Cl-doped Bi2S3 homojunction nanorods with rich-defects for collaboratively boosting photocatalytic reduction performance. Appl Surf Sci 529:147002 Zhou G, Long L, Wang P, Hu Y, Zhang Q, Liu C (2020) Designing CuO/ZnO nanoforest device toward optimal photocatalytic performance through structure and facet engineering. Mater Lett 273:127907 Carvalho LM, Soares AF, Lima MS, Cruz-Filho JF, Dantas TCM, Luz GE (2021) 2,4-Dichlorophenoxyacetic acid (2,4-D) photodegradation on WO3-TiO2-SBA-15 nanostructured composite. Environ Sci Pollut Res 28(7): 7774–7785 Li J, Du X, Yao L, Zhang Y (2014) Synthesis of SnS2/WO3 nanocomposite with enhanced photocatalytic activity. Mater Lett 121:44–46[ Shi J, Liao R, Jia R, Liu Y, Wu D, Chang S, Zhang N, Gao G, Wang X, Hu D, Wu K (2023) A novel combustion drying synthesis route of 3D WO3–SiO2 composite aerogels for enhanced adsorption and visible light photocatalytic activity. J Non-Cryst Solids 609:122259 Zhang J, Guo Y, Xiong Y, Zhou D, Dong S (2017) An environmentally friendly Z-scheme WO3/CDots/CdS heterostructure with remarkable photocatalytic activity and anti-photocorrosion performance. J Catal 356:1–13 Dozzi MV, Marzorati S, Longhi M, Coduri M, Artiglia L, Selli E (2016) Photocatalytic activity of TiO2-WO3 mixed oxides in relation to electron transfer efficiency. Appl Catal B-Environ 186:157–165 Ali AM, Ismail AA, Bouzid H, Harraz FA (2014) Sol–gel synthesis of ZnO–SiO2 thin films: impact of ZnO contents on its photonic efficiency. J Sol-Gel Sci Technol 71:224–233 Yao L, He JH (2014) Facile dip-coating approach to fabrication of mechanically robust hybrid thin films with high transmittance and durable superhydrophilicity. J mater Chem A 2(19):6994–7003 Li Y, Yang K, Xia B, Yang B, Yan L, He M, Yan H, Jiang B (2017) Preparation of mechanically stable triple-layer interference broadband antireflective coatings with self-cleaning property by sol–gel technique. RSC Adv 7, 14660–14668. Thilagavathi T, Venugopal D, Marnadu R, Chandrasekaran J, Alshahrani T, Shkir M (2021) An Investigation on Microstructural, Morphological, Optical, Photoluminescence and Photocatalytic Activity of WO(3) for Photocatalysis Applications: An Effect of Annealing. J Inorg Organomet Polym Mater 31(3):1217–1230 Wang M, Kim EJ, Chung JS, Shin EW, Hahn SH, Lee KE, Park C (2006) Influence of annealing temperature on the structural and optical properties of sol–gel prepared ZnO thin films. Phys Status Solidi A-Appl Mat 203:2418–2424 Ren YF, Li WT, Cao ZH, Jiao YP, Xu JJ, Liu P, Li S, Li X (2020) Robust TiO2 nanorods-SiO2 core-shell coating with high-performance self-cleaning properties under visible light. Appl Surf Sci 509:145377 Saravanan S, Dubey D, Raghvendra S (2020) Synthesis of SiO2 Nanoparticles by Sol-Gel Method and Their Optical and Structural Properties. Rom J Inf Sci Technol 23:105–112 Gui-Long X, Changyun D, Yun L, Pi-Hui P, Jian H Zhuoru Y (2011) Preparation and characterization of Raspberry-like SiO2 particles by the sol-gel method. Nanomater Nanotechnol 1:21 Boran F, Çetinkaya S (2017) Synthesis, Characterization and Sensing Behavior of WO₃ Nanocrystalline Powder for Toluene Vapor. Acta Phys Pol A 132(3):572–573 Aksoy S, Caglar Y (2019) Synthesis of Mn doped ZnO nanopowders by MW-HTS and its structural, morphological and optical characteristics. J Alloys Compd 781:929–935 Jayarambabu N, Kumari BS, Rao KV, Prabhu YT (2014) Germination and growth characteristics of mungbean seeds (Vigna radiata L.) affected by synthesized zinc oxide nanoparticles. Int J Curr Eng Technol 4(5):3411–3416 Sakthisabarimoorthi A, Dhas SMB, Jose M (2020) Study on optical nonlinearity of Au@ SiO2 composite nanoparticles towards photonic applications. Mater Chem Phys 240:122154 Jerold Antony A, Mary Jelastin Kala S, Joel C, Biju Bennie R, Vivetha S (2022) Structural, optical, and magnetic properties of pristine and Cr doped WO3 nanoparticles. Inorg Nano-Met Chem 52(7):951–960 Li X, He S, Liu X, Jin J, Meng H (2019) Polymer-assisted freeze-drying synthesis of Ag-doped ZnO nanoparticles with enhanced photocatalytic activity. Ceram Int 45(1):494–502 Muljani S, Wahyudi B, Sumada K (2016) Potassium silicate foliar fertilizer grade from geothermal sludge and pyrophyllite. In MATEC Web of Conferences (Vol. 58, p. 01021). EDP Sciences Chahi M, Alcántara SP, Bouhekka A, Sib JD, Sanchez G, Chahed L (2020) The enhancement of near infrared light trapping in solar cells with backside crystalline silicon gratings: Realization and characterization investigation, Optik 200:163142 Farhadian M, Sangpour P, Hosseinzadeh G (2015) Morphology dependent photocatalytic activity of WO3 nanostructures. J Energy Chem 24(2):171–177 Wang SM, Yan XX, Deng DM, He HB, Lei YY, Shen X, Luo LQ (2019) Controllable synthesis and enhanced photocatalytic activity of B-TiO2 nanospheres. Micro Nano Lett 14(7):740–743 Wu T, Li JY, Chang MQ, Song YH, Sun Q, Wang FK, Zou HF, Shi Z (2021) Photoluminescence properties and photocatalytic activities of SiO2@TiO2:Sm3 + nanomaterials. J Phys Chem 149:109775 Hu SZ, Li FY, Fan ZP (2012) Preparation of SiO2-Coated TiO2 Composite Materials with Enhanced Photocatalytic Activity Under UV Light. Bull Korean Chem Soc 33(6):1895–1899 Jourshabani M, Lee BK (2021) Unmasking the Role of an Amorphous/Amorphous Interface and a Crystalline/Amorphous Interface in the Transition of Charge Carriers on the CN/SiO2/WO3 Photocatalyst. ACS Appl Mater Interfaces 13(27):31785–31798 Hamed NKA, Ahmad MK, Hairom NHH, Faridah AB, Mamat MH, Mohamed A, Suriani AB, Soon CF, Fazli FIM, Mokhtar SM (2022) Photocatalytic degradation of methylene blue by flowerlike rutile-phase TiO2 film grown via hydrothermal method. J Sol-Gel Sci Technol 102(3):637–648 Lu C, Zhimin BZ, Qin C, Dai L, Zhu A (2016) Facile fabrication of heterostructured cubic-CuFe2O4/ZnO nanofibers (c-CFZs) with enhanced visible-light photocatalytic activity and magnetic separation. RSC Adv 6:110155–110163 Sharma DK, Purohit G (2014) Analysis of the effect of fill factor on the efficiency of solar PV system for improved design of MPPT. In 6th world conference on photo voltaic energy conversion Author informations Ankara University, Engineering Faculty, Energy Systems Engineering, Ankara, 06830, TURKEY Ozcan Koysuren, Savas Yaglikci, Bilge Tuncel Polytechnic University of Tirana, Faculty of Mechanical Engineering, Department of Production and Management, Tirana, 1001, ALBANIA Klodian Dhoska, Irida Markja, Kirsehir Ahi Evran University, Faculty of Engineering and Architecture, Department of Environmental Engineering, Kirsehir, 40100, TURKEY Hafize Nagehan Koysuren Polytechnic University of Tirana, Faculty of Mechanical Engineering, Energy Department, Tirana, 1001, ALBANIA Elena Bebi Corresponding Author Correspondence to Ozcan Koysuren or Klodian Dhoska Statements & Declarations Additional Declarations No competing interests reported. Supplementary Files Graphicalabstract.png SupplementaryInformationPublication.docx Cite Share Download PDF Status: Published Journal Publication published 06 Mar, 2024 Read the published version in Journal of Sol-Gel Science and Technology → Version 1 posted Editorial decision: Revision requested 31 Jan, 2024 Reviews received at journal 26 Jan, 2024 Reviewers agreed at journal 14 Jan, 2024 Reviews received at journal 08 Jan, 2024 Reviewers agreed at journal 05 Jan, 2024 Reviewers agreed at journal 29 Dec, 2023 Reviewers invited by journal 12 Dec, 2023 Editor assigned by journal 05 Dec, 2023 Submission checks completed at journal 05 Dec, 2023 First submitted to journal 04 Dec, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3704926","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":256421010,"identity":"e1b7f9de-e1bf-4cdd-ab46-27d6f7f3b3e0","order_by":0,"name":"Ozcan Koysuren","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIie3OMWsCMRTA8Qc32CFya8IVP0MgcJPoV2kIdApSEERwsOBwS+BWBz+EInS64RWht1z3G51uyqA4CYV6Qgs6GG90yH8I7xF+JAA+3wNG/4cQIPgbXxoS9n5JsAnh2JSwxIhDO+sORP694cesB2FL82Cf3SYRKeKIVK/DuBgoaSoFzFgOWN0mHarjgOBGfqAWSDAAXuqaOH5WE3Eg+CvXqRWfPziF/j0SUc0jgiiXtVX1c8DpHcLM14gtUMl5aYV4xpzQonrDwkFoPlvvLPZkmmrBLE46YaJW27GDADzxq5WcDycAaG3d9z6fz+c7AY9BVLHDZZq8AAAAAElFTkSuQmCC","orcid":"","institution":"Ankara University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Ozcan","middleName":"","lastName":"Koysuren","suffix":""},{"id":256421011,"identity":"ccc429a7-8ae5-4121-992f-b56b8cc4ff49","order_by":1,"name":"Klodian Dhoska","email":"","orcid":"","institution":"Polytechnic University of Tirana","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Klodian","middleName":"","lastName":"Dhoska","suffix":""},{"id":256421014,"identity":"1e669ad6-3ac3-4ade-8cdb-597b6941f6f0","order_by":2,"name":"Hafize Nagehan Koysuren","email":"","orcid":"","institution":"Kirsehir Ahi Evran University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hafize","middleName":"Nagehan","lastName":"Koysuren","suffix":""},{"id":256421016,"identity":"64f6c2d9-3b6a-4c9d-8af9-9d553b6d40f8","order_by":3,"name":"Irida Markja","email":"","orcid":"","institution":"Polytechnic University of Tirana","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Irida","middleName":"","lastName":"Markja","suffix":""},{"id":256421018,"identity":"d0c0b839-b536-4b2f-b175-9606fcf4c1b8","order_by":4,"name":"Savas Yaglikci","email":"","orcid":"","institution":"Ankara University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Savas","middleName":"","lastName":"Yaglikci","suffix":""},{"id":256421019,"identity":"a51a077f-aa75-4991-a41c-6c6a988d7828","order_by":5,"name":"Bilge Tuncel","email":"","orcid":"","institution":"Ankara University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Bilge","middleName":"","lastName":"Tuncel","suffix":""},{"id":256421020,"identity":"09427beb-6958-4ace-8428-c57b549ea83e","order_by":6,"name":"Elena Bebi","email":"","orcid":"","institution":"Polytechnic University of Tirana","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Elena","middleName":"","lastName":"Bebi","suffix":""}],"badges":[],"createdAt":"2023-12-04 08:44:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3704926/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3704926/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10971-024-06351-7","type":"published","date":"2024-03-06T15:01:58+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":47798785,"identity":"9b4ffdb3-01b2-4116-871e-ee61a40be9bb","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1092470,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectrum of (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/06ce6c9b1caf7f772a0a5003.png"},{"id":47798786,"identity":"efe8deff-6777-485b-ac05-0f3cdc3ee5a5","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1161177,"visible":true,"origin":"","legend":"\u003cp\u003eXRD spectrum of (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/726c7c06d488ec23e6ed409b.png"},{"id":47801733,"identity":"c7aad8f2-2d61-4510-9cf3-ae108d437f02","added_by":"auto","created_at":"2023-12-07 15:38:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":12787622,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM image and EDX spectrum of (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e and (c) ZnO films\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/ec704dbcd73da30d9a215553.png"},{"id":47801034,"identity":"90a5fdca-29a2-4285-a6d6-3ca1400d1d66","added_by":"auto","created_at":"2023-12-07 15:30:42","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":6602702,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM image and EDX spectrum of (a) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and (b) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/9c1a9a37bda78258213581b9.png"},{"id":47801038,"identity":"e5931cd4-25e6-45d2-83e8-b9e620c7054f","added_by":"auto","created_at":"2023-12-07 15:30:42","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":20529632,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microscopy image of\u003cstrong\u003e \u003c/strong\u003e(a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/9cd6b6872a87102c2236cb13.png"},{"id":47798798,"identity":"f6dd7435-aef4-45b6-9750-43014acbd416","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2773214,"visible":true,"origin":"","legend":"\u003cp\u003eTransmittance spectrum of (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20), (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30), (f) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40), (g) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50), (h) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), (i) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70), (j) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80), (k) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), (l) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20), (m) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) and (n) uncoated glass slide\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/d98aaaf073181049e41033b6.png"},{"id":47801732,"identity":"e2871798-f98f-4e08-8e89-f9c1a1585b30","added_by":"auto","created_at":"2023-12-07 15:38:42","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2029043,"visible":true,"origin":"","legend":"\u003cp\u003eAbsorbance spectrum of (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20), (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30), (f) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40), (g) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50), (h) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), (i) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70), (j) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80), (k) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), (l) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) and (m) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30)\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/0c93b9de4f8b31ae0b09a593.png"},{"id":47798791,"identity":"3e14795a-5c6b-4f8c-b765-bd4ce3f91188","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1412121,"visible":true,"origin":"","legend":"\u003cp\u003ePhotocatalytic degradation of methylene blue on (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20), (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30), (f) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40), (g) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50), (h) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), (i) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70), (j) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80) films\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/d4ef85f63182c90b020894b2.png"},{"id":47798797,"identity":"ffee9f4b-50ff-436c-a485-b4341e6b2605","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1763939,"visible":true,"origin":"","legend":"\u003cp\u003eProposed photocatalytic reduction mechanism of methylene on (a) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film and (b) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film\u003c/p\u003e","description":"","filename":"Fig9.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/672e224df2c4d5b5ac351f2c.png"},{"id":47798789,"identity":"680225b6-3f1d-478f-9d93-d36fc24740b9","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":546441,"visible":true,"origin":"","legend":"\u003cp\u003ePhotocatalytic degradation of methylene blue on (a) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), (b) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) and (c) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e","description":"","filename":"Fig10.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/d922eb74f560074e1ddba19d.png"},{"id":47803457,"identity":"c5d6fde7-867d-4a2d-a3a0-54f115be1a76","added_by":"auto","created_at":"2023-12-07 15:46:42","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1598593,"visible":true,"origin":"","legend":"\u003cp\u003ePhotocatalytic degradation of the model dye on (a) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) (1-fold coating), (b) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) (2-fold coating), (c) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) (3-fold coating), (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (1-fold coating), (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (2-fold coating) and (f) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (3-fold coating) films under the UVA light irradiation\u003c/p\u003e","description":"","filename":"Fig11.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/9912386dd2bc60299e9cfaa5.png"},{"id":47798795,"identity":"12aa6356-5589-4e07-8954-45b734c1c9b5","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":2387039,"visible":true,"origin":"","legend":"\u003cp\u003eCurrent-voltage characteristics of solar cell coated with (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) WO\u003csub\u003e3\u003c/sub\u003e, (c) ZnO, (d) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20), (e) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30), (f) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40), (g) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50), (h) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), (i) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70), (j) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80), (k) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), (l) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20), (m) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films and including (n) uncoated glass slide\u003c/p\u003e","description":"","filename":"Fig12.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/548c0b74c989f77809ae1712.png"},{"id":47798792,"identity":"d66c2eeb-1e5d-46a5-90ba-54a21ddfc8c3","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":481752,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in water contact angle with the irradiation time on (a) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and (b) SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e","description":"","filename":"Fig13.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/df8bbde9e3093e09268ac3f9.png"},{"id":52432099,"identity":"f7dc7d6d-b0c6-48df-82e3-7e755abae64c","added_by":"auto","created_at":"2024-03-11 15:10:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5811978,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/d6f9d1bb-cc42-443a-87c0-af80273d6820.pdf"},{"id":47798787,"identity":"5071b08f-0b25-4f8c-ad8c-4788b039b519","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1294728,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.png","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/f9bccb0cbcb0c3251d5b908a.png"},{"id":47798799,"identity":"95f02e69-951a-468c-8b4e-a5ae7b65bf7e","added_by":"auto","created_at":"2023-12-07 15:22:42","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3295566,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformationPublication.docx","url":"https://assets-eu.researchsquare.com/files/rs-3704926/v1/b7dc1e68cea0e885875c7216.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"SiO2 /WO3 /ZnO Based Self-cleaning Coatings for Solar Cells","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eCoupling WO\u003csub\u003e3\u003c/sub\u003e with SiO\u003csub\u003e2\u003c/sub\u003e and ZnO provided enhancement in the photocatalytic activity.\u003c/li\u003e\n \u003cli\u003eThe photocatalytic dye removal efficiency was improved to over 90% with SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film under UVA light irradiation.\u003c/li\u003e\n \u003cli\u003eThe light transparency of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film in the visible light spectrum was almost 5% lower than that of the cover glass of a solar cell.\u003c/li\u003e\n \u003cli\u003eThere was a decrease in the water contact angle due the photocatalytic degradation of the model contaimination on the film coating under the UVA light irradiation.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Introduction","content":"\u003cp\u003eSelf-cleaning coatings are found in a wide variety of applications such as solar cell panels, electronic and optical device panels, window glass, textiles and paints. Self-cleaning coatings contribute to reducing the efficiency lost of the solar cell, cleaning costs and maintaining stability of all surfaces. Self-cleaning coatings fall into two categories: hydrophobic and hydrophilic coatings [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. A surface with a water contact angle greater than 90\u0026deg; is considered as hydrophobic. On the hydrophobic surfaces, water droplets take the shape of a sphere and clean the surface by rolling the formed droplets [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. On the other hand, for hydrophilic surfaces with a water contact angle less than 90\u0026deg;, the self-cleaning mechanism occurs by photocatalytic degradation of the pollutants under UV radiation and then the removal of the contaminations formed on the surface with water. Semiconductor photocatalysts such as ZnO and TiO\u003csub\u003e2\u003c/sub\u003e can be added to the surface coatings to make the surface hydrophilic [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Photocatalytic degradation, which is part of the self-cleaning process on hydrophilic surfaces, is the decomposition of organic compounds into small molecules such as CO\u003csub\u003e2\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO. In photocatalytic degradation reactions, light with energy equal to or greater than the optical band gap energy of the photocatalyst can be absorbed by the photocatalyst. In this case, electrons in the valence band of the photocatalyst are excited and transferred to the conduction band. The electron vacancies, called as holes (h\u003csup\u003e+\u003c/sup\u003e), formed in the valence band of the photocatalyst, which can oxidize the surface adsorbed water molecule and turn it into a hydroxyl radical; the electrons excited to the conduction band can reduce the surface adsorbed O\u003csub\u003e2\u003c/sub\u003e molecule and convert it to a superoxide radical. Both active radicals formed allow the degradation of organic pollutants adsorbed to the surface of the solar cell panel [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the literature, different semiconductor photocatalysts such as TiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], ZnO [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], KWO\u003csub\u003e3\u003c/sub\u003e [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] and Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] have been used to develop self-cleaning coatings based on the photocatalytic activity. Several studies from the literature have been summarized on Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Self-cleaning by semiconductors takes place through the photocatalytic and the hydrophilicity mechanisms. The photocatalytic mechanism results to degradation of the polutions while the hydrophilicity mechanism laminates the water droplets on the surface to wash the degraded pollution, preventing the adhesion of the pollutants on the surface. In literature, Khorshidi and his coworkers (2021) measured the water contact angle on the acylic/ZnO coating, deposited with a model pollutant (stearic acid). Under the UV light, the stearic acid molecules degraded into H\u003csub\u003e2\u003c/sub\u003eO and CO\u003csub\u003e2\u003c/sub\u003e. H\u003csub\u003e2\u003c/sub\u003eO as a degradation product might decrease the water contact angle of the coating about 22\u0026deg; in 135 min. Hence, a decrease in the water contact angle might exhibit the potential of the photocatalytic activity and the cleaning of the coating surface [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSelf-cleaning surface studies based on the photocatalytic activity from the literature\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCoated Surface\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePhotocatalyst\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eResults\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBuilding material (concrete surface) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, BiOI, BiVO\u003csub\u003e4\u003c/sub\u003e, BiPO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e49% pollution (model dye) removal after 3 hours with Bi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePolymer (PMMA) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eApproximately 80% dye removal after 3 hours\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlass surface [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eKWO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29% dye removal after 2 hours\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCement mortar [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e/ZnAl layered double hydroxide\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReduction in water contact angle about 90\u0026deg; in 210 min.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlass surface [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWO\u003csub\u003e3\u003c/sub\u003e/TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.6% achievement in energy output gain after 8 months\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlass surface [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e/SiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReduction in water contact angle from 90\u0026deg; to 20\u0026deg; in 70 h.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlass surface [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCu-TiO\u003csub\u003e2\u003c/sub\u003e, Ag-TiO\u003csub\u003e2\u003c/sub\u003e, Fe-TiO\u003csub\u003e2\u003c/sub\u003e and Co-TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e77%, 74%, 76% and 69% pollution (model dye) removal after 2 hours with Cu-TiO\u003csub\u003e2\u003c/sub\u003e, Ag-TiO\u003csub\u003e2\u003c/sub\u003e, Fe-TiO\u003csub\u003e2\u003c/sub\u003e and Co-TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlass surface [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAcrylic/ZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eReduction in water contact angle from 90.2\u0026deg; to 68.1\u0026deg; in 135 min.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlass surface [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e/Kaolin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65% dye removal after 210 min.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe change in hydrophilic property of a solid surface with light radiation is related to the change in surface energy. There are different assumptions about determining the reasons of changes in surface energy at the atomic level. According to an assumption, the hydrophilic property of the solid surface increases with the contribution of organic pollution products that decompose under light. This is explained by the formation of metastable nano-sized hydrophilic regions on the surface due to the transport of the photogenerated electron-hole pairs to the solid surface. The second hypothetical mechanism of the photo-induced hydrophilic transformation of a surface is related to the thermal effect of light. This effect causes water bound by weak bonds in the outer layers of the solid surface to separate from the surface. Thus, the surface energy and thus the hydrophilicity of the solid increases. Then, water molecules spread on the solid surface, forming a film layer. Re-adsorption of water restores the initial structure of the hydrated layer and thus reduces the surface energy [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe sun provides free heat and electricity for real-life applications. In addition, the solar energy is environmentally friendly and it does not produce any emissions. For this reason, solar energy could be the most suitable and sustainable solution to the energy crisis of the World. However, several problems hinder optimum power harvesting from the photovoltaic (PV) modules. Dust accumulation on the surface of the PV module has been known as one of the crucial problems of the PV systems [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. As it is known, the light-permeable surface of the solar cell can be easily contaminated due to the adhesion of dust, organic pollutants and inorganic particles. Accordingly, the light transmittance of the surface and the light absorption of the solar cell could reduce. In addition, cleaning the contaminated surface requires extra labor and money. There is also the possibility of scratching and damaging the surface during the cleaning. Therefore, the removal of the surface adsorbed polution from the PV panel is of great importance [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. There are three different self-cleaning methods, applied to clean the PV panels. Electrostatic, mechanical and coating methods are among these techniques to clean the surfaces of the PV panels, which are exposed to the outdoor conditions. The electrostatic method throws out the dust from the surface through the electrostatic wave. The mechanical method consists of four techniques, robotic method, air blowing method, water blowing method and ultrasonic vibration method, to expel surface adsorbed dust. The coating method technology is based on forming a thin layer of film coating, which can be either hydrophilic or hydrophobic. The hydrophilic coating reduces the surface pollution through a photocatalytic degradation reaction, while the hydrophobic coating rolls the water droplet to remove the pollution from the surface of the PV panel [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The accumulation of the pollution and its effect on the effiency of the PV cell depends on the tilt angle of the PV system, the exposure duration, the climate conditions like the wind condition, the pollution density and the surface material of the PV system [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTungsten oxide (WO\u003csub\u003e3\u003c/sub\u003e) has been utilized as a photocatalyst for the degradation of the organic pollutants under the UV light irradiation. WO\u003csub\u003e3\u003c/sub\u003e as a photocatalyst has important features like nontoxicity and chemically stability. Also, WO\u003csub\u003e3\u003c/sub\u003e exhibits high resistance against acids and it has high photocorrosion resistance [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Due to the specified properties, WO\u003csub\u003e3\u003c/sub\u003e is preferred in gas sensors, photochromic and electrochromic device applications. WO\u003csub\u003e3\u003c/sub\u003e can also be thought as an appropriate anode material in the photoelectrochemical water splitting reactions [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Although WO\u003csub\u003e3\u003c/sub\u003e can absorb the entire range of the UV light spectrum, the recombination rate of the photoinduced charge carriers, generated on WO\u003csub\u003e3\u003c/sub\u003e, is high [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Forming a p-n heterojunction within the composite structure is a best solution to suppress the recombination of the photoinduced charge carriers and subsequently to enhance the photocatalytic activity. When n type and p type semiconductors are brought together to provide a stable contact, an electric field will be generated between the semiconductors, providing the reverse transfer of the charge carriers. The electric field provides the separation of the photoinduced charge carriers between the semiconductors [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In literature, several studies have been conducted to promote the separation of the photogenerated electron-hole pairs on WO\u003csub\u003e3\u003c/sub\u003e such as WO\u003csub\u003e3\u003c/sub\u003e/TiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], WO\u003csub\u003e3\u003c/sub\u003e/SnS\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], WO\u003csub\u003e3\u003c/sub\u003e/SiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], WO\u003csub\u003e3\u003c/sub\u003e/CdS [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. By coupling WO\u003csub\u003e3\u003c/sub\u003e with another semiconductor possessing a valence band edge and a conduction band edge more positive or more negative in level than the valence band edge or the conduction band edge of WO\u003csub\u003e3\u003c/sub\u003e, the photoexcited holes or electrons can move between the bands of the semiconductor and WO\u003csub\u003e3\u003c/sub\u003e, suppressing the recombination of the photoinduced charge carriers on the semiconductor and WO\u003csub\u003e3\u003c/sub\u003e. This event can enhance the photocatalytic activity [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In the scope of the study, WO\u003csub\u003e3\u003c/sub\u003e was combined with SiO\u003csub\u003e2\u003c/sub\u003e in the composite film structure. The sol\u0026ndash;gel technique, known as one of the most efficient methods to prepare the composite films, was applied to prepared SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite films. The sol-gel technique is relativelty simple and a low-cost process when compared with the deposition methods applied under vacuum [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Also, ZnO was added into the composite film to enhance the photocatalytic activity and subsequently the self-cleaning property. The application potential of SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films as a self-cleaning coating on a real solar cell was studied. There were some challenges to be removed before the self-cleaning coatings could be used in practical application. ZnO and WO\u003csub\u003e3\u003c/sub\u003e exhibit the light-induced superhydrophilicity and these semiconductors exhibit photocatalytic activity under UV light irradiation. When exposed to the UV light, ZnO or WO\u003csub\u003e3\u003c/sub\u003e can degrade any kinds of organic contaminants or pollution adhering to the surface of the glass cover of the PV panel. The UV-induced superhydrophilic property of ZnO and WO\u003csub\u003e3\u003c/sub\u003e allows water droplets to spread and flow on the surface of the cover glass, contributing to the self-cleaning process. Combining the self-cleaning process and the photocatalytic activity within a coating is of great importance in terms of the solar energy technology [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. However, ZnO or WO\u003csub\u003e3\u003c/sub\u003e coatings on the glass cover of the PV panel could reduce the transmittance owing to their relatively high refractive index (n\u0026thinsp;=\u0026thinsp;2 for ZnO and n\u0026thinsp;=\u0026thinsp;1.9 for WO\u003csub\u003e3\u003c/sub\u003e) compared to SiO\u003csub\u003e2\u003c/sub\u003e (n\u0026thinsp;=\u0026thinsp;1.5) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. On the other hand, SiO\u003csub\u003e2\u003c/sub\u003e with a low refractive index and low surface scattering is beneficial and effective in improving the light transmission for the glass cover of the PV panel. In addition, SiO\u003csub\u003e2\u003c/sub\u003e film exhibits hydrophilicity and self-cleaning properties owing to the presence of hydroxyl groups in its chemical structure [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. However, the superhydrophilicity of a SiO\u003csub\u003e2\u003c/sub\u003e film coated on the cover glass of the PV panel may reduce in time owing to deposition of dust and organic pollutants, and the photocatalytic activity of SiO\u003csub\u003e2\u003c/sub\u003e is low [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The optimization of the coated film in terms of the specified features is a significant and a detailed study was conducted to achieve a balance between the specified properties. In literature, there is no study on the self-cleaning effect of SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films for solar cells.\u003c/p\u003e \u003cp\u003eExperimental\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e, WO\u003csub\u003e3\u003c/sub\u003e and ZnO solutions were prepared separately to prepare SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films. To prepare the SiO\u003csub\u003e2\u003c/sub\u003e solution, tetraethylorthoxylsilicane (TEOS) (112 ml) was mixed with a certain amount of distilled water-anhydrous ethanol solution (36 ml-1090 ml). Then, concentrated hydrochloric acid solution (~\u0026thinsp;0.2 ml, 36%) was added into the solution to obtain a final molar ratio of TEOS : ethyl alcohol : H\u003csub\u003e2\u003c/sub\u003eO : HCl as 1 : 37.5 : 4 : 0.004. The expected concentration of SiO\u003csub\u003e2\u003c/sub\u003e within the final solution was 3 wt%. The solution will be stirred in a closed glass vessel at the room temperature for 2 h. and held in the dark for 1 day [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]. To prepare the WO\u003csub\u003e3\u003c/sub\u003e solution, sodium tungstate dihydrate (Na\u003csub\u003e2\u003c/sub\u003eWO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO) (3 g) was dissolved in 20 ml of distilled water and stirred at the room temperature. HCl solution (20 ml, 8 M) was added into the prepared solution. Then, the solution was stirred for 2 h at 80\u0026deg;C. After cooling to room temperature, the as-prepared solution was held in the dark for 1 day [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. On the other hand, zinc acetate 2-hydrate (Zn(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO) was used as a precursor of Zn atom to prepare the ZnO solution. Absolute ethanol and diethanolamine were used as a solvent and a solution stabilizer, respectively. In detail, 0.05 mol of Zn(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO was dissolved in ethanol (100 ml) to obtain 0.5 M solution. The as-prepared solution was stirred for half an hour. Then, 0.05 mol of the solution stabilizer was added into the solution under stirring. Afterward, the solution was stirred for 30 min. The as-prepared solution was held in the dark for 1 day [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\n\u003cp\u003eThe SiO\u003csub\u003e2\u003c/sub\u003e solution and the WO\u003csub\u003e3\u003c/sub\u003e solution was mixed with varying ratios (80/20, 70/30, 60/40, 50/50, 40/60, 30/70 and 20/80 wt./wt.) to obtain the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite solutions. The composite solutions were stirred for 2 h and held in the dark for 1 day. Within the scope of the optimization study, the optimum SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composition was determined by using the photocatalytic activity measurements. The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film composition, resulted the highest photocatalytic activity, was determined and the optimum SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composition was used in the remaining studies to prepare the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO composites. In addition, the ZnO solution was mixed with varying ratios ((SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e)/ZnO : 70/30, 80/20 and 90/10 wt./wt.) with the optimum SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e solution to prepare the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO composites. The composite films were labed as SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(x/y) based on the weight ratio of SiO\u003csub\u003e2\u003c/sub\u003e to WO\u003csub\u003e3\u003c/sub\u003e. In addition, the composite films were labed as SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(x/y) based on the weight ratio of SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e to ZnO. Ultrasonic cleaning was applied to the glass substrates prior to the dip-coating process. The as-prepared solutions were deposited on the glass substrates through the dip-coating technique at the ambient condition. After the dip-coating process, the glass substrate was dried at the ambient condition for 2 h. The as-deposited film was pre-heated at 100\u0026deg;C for 1 h to remove the unreacted volatile species. Afterward, it was annealed at 400\u0026deg;C for 2 h to provide the growth of the crystalline phase [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]. As a process parameter, the number of the dip-coating cycle was changed to investigate the effect of the film thickness on the photocatalytic activity, the light transmittance ratio and the efficiency loss of the solar cell.\u003c/p\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003eStructural, morphological and optical characterization\u003c/h2\u003e\n\u003cp\u003eFourier transform infrared (FTIR) spectra of the film samples was be obtained by scanning between the wavenumber range of 4000 to 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using a Bruker IFS 66/S model FTIR spectrophotometer with a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. It was planned to evaluate the chemical bond structures of the photocatalyst systems using the FTIR spectrocopy. X-ray diffraction (XRD) patterns of the film samples was recorded to identify the crystal structure. A Rigaku Ultima IV model X-ray diffractometer was used with monochromatic Cu K\u0026alpha; radiation (\u0026lambda;\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;) at a scan rate of 1\u0026deg;/min. The morphology of the coated films was examined with a QUANTA 400F fied emission scanning electron microscope (FESEM). A conductive coating was deposited on the samples prior to the analysis. The distribution and the interaction of the composite constituents within the composite structure was examined using the FESEM images. The elemental composition of the film samples was investigated by energy dispersive X-ray (EDX) spectroscopy (JXA-8230 EDX Microanalysis Instrument).\u003c/p\u003e\n\u003cp\u003eThe transmittance and absorbance spectrum of the coated films were recorded in the wavelength range of 200 nm to 800 nm using a Genesys 10S (Thermo Scientific) model spectrophotometer. The UV-Vis absorbance spectrum was used to determine the optical band gap of the coated film by using the Tauc equation given below [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e]:\u003c/p\u003e\n\u003cp\u003e\u0026alpha;hʋ = A(hʋ - Eg)\u003csup\u003e1/2\u003c/sup\u003e (1)\u003c/p\u003e\n\u003cp\u003eat which \u0026alpha;, Eg and hʋ are the absorption coefficent, the optical band gap energy and the photon energy, respectively. The optical band gap energy was estimated by extrapolating the linear part of the curve to the x-axis on the plot of (\u0026alpha;h\u0026nu;)\u003csup\u003e2\u003c/sup\u003e vs. hv.\u003c/p\u003e\n\u003cp\u003eThe film coatings should not reduce the efficiency of the solar cell due to a possible decrease in the solar light transmittance. The negative effects of self-cleaning coatings on the efficiency of the solar cell was also examined in the scope of this study. Most of the studies conducted on the self-cleaning coatings for the PV system have neglected to measure the efficiency loss that might occur in the solar cell. The efficiency of the self-cleaning coated solar cell and the uncoated solar cell was compared. The efficiency of a solar cell was calculated using the following equation:\u003c/p\u003e\n\u003cp\u003e\u0026eta; (efficiency)\u0026thinsp;=\u0026thinsp;V\u003csub\u003eOC\u003c/sub\u003e I\u003csub\u003eSC\u003c/sub\u003e FF / P\u003csub\u003ein\u003c/sub\u003e (2)\u003c/p\u003e\n\u003cp\u003ewhere V\u003csub\u003eOC\u003c/sub\u003e is the open-circuit voltage, I\u003csub\u003eSC\u003c/sub\u003e is the short-circuit voltage and FF is the fill factor. The glass substrate coated with the self-cleaning coating was placed on the top of a solar cell and the efficiency of this solar cell was measured. As a reference, an uncoated glass substrate was also placed on the top of the solar cell and the efficiency was measured.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003eCharacterization of the Cr(VI) photoreduction performance\u003c/h2\u003e\nThe photocatalytic activity of the as-prepared coatings, soiled with a model organic compound (methylene blue), was monitored under UVA light irradiation (12 W). For this purpose, the coated film samples were immersed into the methylene blue solution (10 mg/l) and then dried in the air atmosphere. The coatings adsorbed with methylene blue will be irradiated with UVA light and at certain time intervals (30 min.), the degradation of methylene blue on the coatings was evaluated by measuring the reduction in the absorbance maximum peak of the model compound (664 nm) using a Genesys 10S model (Thermo Scientific) spectrophotometer by the following equation [\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e]:\u003cbr /\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDegradation efficiency (%) = (A\u003csub\u003e0\u003c/sub\u003e-A)/A\u003csub\u003e0\u003c/sub\u003e (3)\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ewhere A\u003csub\u003e0\u003c/sub\u003e is the initial absorbance of methylene blue and A is the absorbance of methylene blue after the UV light irradiation. In addition, the photocatalytic activity of the optimum SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films was analyzed using the water contact angle measurement. Photocatalytic degradation of a model dye, methyl stearate, on the coated surface has been reported in the literature by Ren et al. (2020). According to the method described, methylene blue was dissolved in distilled water (10 mg/l) and it was tried to be adsorbed on the coated films by the dip coating technique. The sample containing the organic pollutant was then exposed to the UVA light. The degradation of the organic pollutant was observed by measuring the water contact angle on the glass surface at certain time intervals (30 min). The contact angle measurement of the water drop was performed at 3 different points on the coating surface according to the fixed drop (sessile drop) method using an optical tensiometer (Theta Lite, Biolin Scientific) [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eFTIR analysis\u003c/h2\u003e \u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, FTIR absorbance spectrum confirmed the successful synthesis of SiO\u003csub\u003e2\u003c/sub\u003e. There is a broad band on the FTIR spectrum of SiO\u003csub\u003e2\u003c/sub\u003e from 2800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 3800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, assigned to the presence of the O-H group [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In addition, there is a weak absorbance peak at 1623 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, assigned to the O-H stretching bond [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. On the other hand, there are strong absorbance peaks at 453 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 819 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1074 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to the asymmetric and symmetric Si-O-Si stretching vibrations [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The weak absorbance peak at 1378 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e might be due to the C-H bond of the SiO\u003csub\u003e2\u003c/sub\u003e precursor (TEOS) [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. On the FTIR spectrum of pure WO\u003csub\u003e3\u003c/sub\u003e film (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), there is a broad absorbance band at around 590 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a sharp absorbance peak at around 800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which were attributed to the W\u0026thinsp;=\u0026thinsp;O stretching bond and the O-W-O stretching bond, respectively [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. FTIR spectrum of pure ZnO film illustrates characteristic peak of ZnO at 482 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 555 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which were attributed to the Zn-O stretching vibrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In addition, there are additional peaks at 865 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1039 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1392 cm-1 and 1629 cm-1, which were assigned to the symmetric bending of the H-O-H bond, the stretching vibration of the C-O bond of the primary alcohol, the secondary alcohol vibration and the vibration mode of alkyls, respectively [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Also, there is a wide absorbance band at around 3438 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and peaks at 2896 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 2975 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to the to the stretching vibration of hydroxyl compounds [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, FTIR absorbance spectrum of the composite film sample confirmed the successful synthesis of both SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e together. The characteristic absorbance peaks of WO\u003csub\u003e3\u003c/sub\u003e were observed at 667 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 966 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, assigned to the W\u0026thinsp;=\u0026thinsp;O stretching bond [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The spectrum also presents the characteristic peak of WO\u003csub\u003e3\u003c/sub\u003e at 957 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, belonging to the stretching of short W\u0026thinsp;=\u0026thinsp;O bonds of WO\u003csub\u003e3\u003c/sub\u003e.H\u003csub\u003e2\u003c/sub\u003eO. On the other hand, the characteristic peaks of SiO\u003csub\u003e2\u003c/sub\u003e were observed at 467 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 797 cm-1 and 1083 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to the Si-O-Si stretching vibrations [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. In addition, there is a weak absorbance peak at 1629 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was attributed to the Si-OH vibrations [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. FTIR spectrum exhibits a broad band at around 3410 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e due to the O-H group [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. On the FTIR spectrum of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee), the characteristic absorbance peak of SiO\u003csub\u003e2\u003c/sub\u003e due to the Si-O-Si stretching vibrations appears at 463 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1067 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The peak present at 515 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e might belong to the Zn-O stretching vibrations [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Characteristic peaks of WO\u003csub\u003e3\u003c/sub\u003e due to the W\u0026thinsp;=\u0026thinsp;O stretching bond and the O-W-O stretching bond are present at 620 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 806 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively, on the same spectrum [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. On the spectrum, there are additional peaks at 871 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1624 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 3445 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3512 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which were attributed to the stretching vibration of hydroxyl compounds [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eXRD analysis\u003c/h2\u003e \u003cp\u003eThe XRD analysis was conducted to investigate the crystal structure of pure and composite film samples. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea illustrates the XRD pattern of the SiO\u003csub\u003e2\u003c/sub\u003e film. The XRD profile of the SiO\u003csub\u003e2\u003c/sub\u003e film exhibited a broad peak at round 23\u0026deg; owing to the formation of amorphous SiO\u003csub\u003e2\u003c/sub\u003e nanoparticles [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, all the peaks on the XRD pattern, in well accordance with the JCPDS No. 83\u0026ndash;0950, might be consigned to the monoclinic WO\u003csub\u003e3\u003c/sub\u003e crystal phase. The more intense peaks at 23.6\u0026deg;, 24.3\u0026deg;, 26.6\u0026deg;, 28.8\u0026deg;, 34.1\u0026deg;, 41.9\u0026deg;, 48.4\u0026deg;, 49.9\u0026deg; and 55.8\u0026deg; corresponding to the (002), (200), (120), (112), (202), (222), (040), (-114) and (142) planes provided a strong evidence for the monoclinic WO\u003csub\u003e3\u003c/sub\u003e phase [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec illustrates the XRD pattern of pure ZnO film. The peaks of the ZnO film belongs to the typical hexagonal wurtzite structure. The diffraction pattern exhibited sharp and intense peaks at 31.9\u0026deg;, 34.5\u0026deg;, 36.4\u0026deg;, 47.7\u0026deg;, 56.7\u0026deg;, 63.0\u0026deg; and 68.1\u0026deg; corresponding to the (100), (002), (101), (102), (110), (103) and (112) planes of the ZnO phase, respectively (JCPDS No. 36-1451) [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. No impurity phase was observed for pure ZnO, revealing the successful synthesis of ZnO in the film structure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed shows the XRD pattern of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample. The XRD pattern exhibited characteristic peaks of the WO\u003csub\u003e3\u003c/sub\u003e phase corresponding to the (002), (200), (120), (112), (202), (222), (040), (-114), (142) and (142) planes at the diffraction angle of 23.6\u0026deg;, 24.3\u0026deg;, 26.6\u0026deg;, 28.6\u0026deg;, 34.1\u0026deg;, 41.8\u0026deg;, 48.3\u0026deg;, 49.9\u0026deg;, 55.7\u0026deg; and 56.4\u0026deg;, respectively. The broad peak belonging to the amorphous SiO\u003csub\u003e2\u003c/sub\u003e structure could not be detected on the XRD pattern of the composite film. Within the composite structure, the amorphous SiO\u003csub\u003e2\u003c/sub\u003e phase might be converted to the crystalline phase. According to the standard card of the crystalline SiO\u003csub\u003e2\u003c/sub\u003e (JCPDS data of 46-1045), there are two characteristic peaks of SiO\u003csub\u003e2\u003c/sub\u003e at 21.1\u0026deg; and 26.6\u0026deg; [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The peak at 21.1\u0026deg; was not present on the XRD pattern of the composite film sample. The peak at 26.6\u0026deg; might be lost in the peak of WO\u003csub\u003e3\u003c/sub\u003e at 26.6\u0026deg;. When compared with pure WO\u003csub\u003e3\u003c/sub\u003e, there was a slight shift in the peak position toward the side of smaller diffraction angle with the composite film structure. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee illustrates the XRD pattern of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film sample. The XRD pattern exhibited characteristic peaks of the WO\u003csub\u003e3\u003c/sub\u003e phase corresponding to the (002), (200), (120), (112), (222), (040), (-114) and (142) planes at 2θ values of 23.8\u0026deg;, 24.5\u0026deg;, 25.9\u0026deg;, 29.9\u0026deg;, 41.3\u0026deg;, 48.3\u0026deg;, 48.7\u0026deg; and 55.6\u0026deg;, respectively. The same pattern included characteristic peaks of the ZnO phase at 31.2\u0026deg;, 33.6\u0026deg;, 36.6\u0026deg;, 47.7\u0026deg;, 64.7\u0026deg; and 68.2\u0026deg;. The characteristic peak belonging to the crystalline SiO\u003csub\u003e2\u003c/sub\u003e phase was present at 21.1\u0026deg;, suggesting that the amorphous SiO\u003csub\u003e2\u003c/sub\u003e phase was converted to the crystalline phase.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMorphological analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the FESEM images of pure SiO\u003csub\u003e2\u003c/sub\u003e, pure WO\u003csub\u003e3\u003c/sub\u003e and pure ZnO film samples. Pure SiO\u003csub\u003e2\u003c/sub\u003e film is homogeneous and without cracks over a wide area. In addition, the SiO\u003csub\u003e2\u003c/sub\u003e film has a smooth surface area. On the other hand, there is no smooth surface area with the WO\u003csub\u003e3\u003c/sub\u003e and ZnO films. There was a significant grain growth on the WO\u003csub\u003e3\u003c/sub\u003e and ZnO film surfaces. The crystal grains were less tightly packed on both of the film surfaces. When compared with the WO\u003csub\u003e3\u003c/sub\u003e film surface, the surface of the ZnO film seems to be smoother. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e also shows the EDX spectrum of pure SiO\u003csub\u003e2\u003c/sub\u003e, pure WO\u003csub\u003e3\u003c/sub\u003e and pure ZnO film samples. The EDX spectroscopy proved the successful synthesis of SiO\u003csub\u003e2\u003c/sub\u003e, WO\u003csub\u003e3\u003c/sub\u003e and ZnO films from their precursor solutions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates the FESEM images of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film and the SiO\u003csub\u003e2\u003c/sub\u003eWO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film samples. The surface structure of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film is similar to the surface structure of pure WO\u003csub\u003e3\u003c/sub\u003e film. There was also a significant grain growth on the composite film surface. The grain structure might belong to the WO\u003csub\u003e3\u003c/sub\u003e phase of the composite film. Compared to pure WO\u003csub\u003e3\u003c/sub\u003e film, the grain structures seem to be smaller. As the WO\u003csub\u003e3\u003c/sub\u003e phase was the dominant phase in the composite, smooth surface areas belonging to the SiO\u003csub\u003e2\u003c/sub\u003e phase were not obvious on the FESEM image of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample. The SiO\u003csub\u003e2\u003c/sub\u003e phase might be embedded into the WO\u003csub\u003e3\u003c/sub\u003e phase, forming a homogeneous SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film layer. On the FESEM image of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film, there was also a significant grain growth. There are two different grain structures in two different sizes. The larger grain structures might belong to the ZnO phase and the smaller grain structure might belong to the WO\u003csub\u003e3\u003c/sub\u003e phase. Compared to the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70), the surface structure of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) seems to be less smooth. EDX spectrum of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film and the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO/70/30) film samples exhibited all the elements of the composite constituents. According to the EDX spectra, both of the composite films were successfully prepared.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the optical microscopy image of the film samples. In all images, there are very few cracks. The cracks, which could occur during the dip coating and drying processes due to the removal of solvent at high speeds, might disappear during the annealing process at 400\u0026deg;C. The dark spherical regions in the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film might belong to the WO\u003csub\u003e3\u003c/sub\u003e phase. The optical microscope images of pure SiO\u003csub\u003e2\u003c/sub\u003e and pure WO\u003csub\u003e3\u003c/sub\u003e films supported this idea. Pure SiO\u003csub\u003e2\u003c/sub\u003e film includes only crack and there are no dark spherical regions. On the other hand, pure WO\u003csub\u003e3\u003c/sub\u003e film includes only a large dark region. According to the optical microscope images, smooth and homogeneous film surfaces were obtained. The optical microscope image of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film is similar to the image of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film. As a difference, there are more dark regions in different sizes. Small-sized and large-sized regions might belong to the WO\u003csub\u003e3\u003c/sub\u003e and ZnO phases, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eLight transmittance study\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the light transmitance spectrum of the film samples. Pure WO\u003csub\u003e3\u003c/sub\u003e film exhibited low transmittance of about 44% between 300\u0026ndash;800 nm, whereas pure SiO\u003csub\u003e2\u003c/sub\u003e film exhibited high transmittance (~\u0026thinsp;92%) in the same region. Hence, an increase in the WO\u003csub\u003e3\u003c/sub\u003e content of the composite film resulted in a reduction in the average transmittance in the whole visible region (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed-\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ej). According to Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed, uncoated glass slide transmitted more UVA light between 320\u0026ndash;470 nm than the glass slide coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20) film. The transparency of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20) film in the visible light spectrum (above 470 nm) was almost 3% higher than that of uncoated glass slide. The reason for the enhancement in the transparency might be the reduced reflectance on the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20) film. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef exhibits the transmittance spectra of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40) film samples. The average transmittance of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40) film samples in the visible light range was almost 85% and 86%, respectively. As compared to uncoated glass slide (91%), the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40) film samples exhibited lower transmittance. The average light transmittance of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50) film in the visible region was around 91%, which was almost the same light transmittance as the uncoated glass slide. The remaining film samples (SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80)) showed average transmittance between 77% and 70% in the visible light region (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eh-\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ej).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) composite film was also combined with ZnO during the dip coating process. Pure ZnO film exhibited nearly high light transmittance (~\u0026thinsp;88%) in the visible light range as the uncoated glass slide. Hence, it was expected that the contribution of the ZnO phase into the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite structure might enhance the light transparency. As expected SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film systems provided higher transmittance than that of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ek). The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10) has an average transmittance of 83% in the visible light region. The transmittance of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples increased with the ZnO content. The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film samples achieved average transmittance of 85% and 87%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003el and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003em). Within the scope of the optimization study, the number of the dip-coating cycle was changed to investigate the effect of the film thickness on the light transparency. Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e exhibits the transmittance spectra of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) film sample. The average transmittance of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) (1-fold coating), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) (2-fold coating) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) (3-fold coating) film samples in the visible light range was almost 72%, 65% and 57%, respectively. In addition, the average transmittance of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (1-fold coating), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (2-fold coating) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (3-fold coating) film samples in the visible light range was almost 87%, 72% and 63%, respectively. When the number of the dip-coating cycle increased, the light transparency decreased for the film samples. With an increase in the numbe of the dip-coating cycle, the film thickness might increase or the film might turn into a denser structure.\u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003eUV-Vis Spectrocopy\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20) film sample exhibited absorption in the UVA light region (315\u0026ndash;400 nm). When the WO\u003csub\u003e3\u003c/sub\u003e content of the film sample increased, the absorption band widened to the visible light region and the optical absorption of the composite film samples in the UVA light region was significantly improved. Pure WO\u003csub\u003e3\u003c/sub\u003e film exhibited absorption in both UV and visible light regions, while pure SiO\u003csub\u003e2\u003c/sub\u003e film exhibited low absorption only in the UV range (~\u0026thinsp;300 nm). As expected WO\u003csub\u003e3\u003c/sub\u003e contribution improved the optical absorption ability of the composite film. It would be appropriate to extend the photocatalytic reaction application to the visible light region. But, it can be detrimental to the solar cell in terms of the efficiency. The photovoltaic market is mainly based on crystalline silicon, which can absorb almost one-third of usable solar photons. Photons in the red and near-infrared portion of the sun light spectrum (700\u0026ndash;1100 nm) can be absorbed by the silicon. Photons with longer wavelengths cannot be absorbed by the silicon. On the other hand, photons with shorter wavelengths can be absorbed by the silicon and they have more energy than the silicon needs, causing the excess energy to be released as heat [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. As specified before WO\u003csub\u003e3\u003c/sub\u003e widened the edge of the absorption band to the visible light, which might lead to a decrease in the intensity of the sun light reaching to the absorber layer of the solar cell. Any decrease in the number of photons in the visible light region (400\u0026ndash;700 nm) might affect the solar cell efficiency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs estimated from the Tauc plot (Fig S2), the optical band gap energy of pure SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e films were estimated to be 4.80 eV and 2.35 eV, respectively. According to Fig. S3, the optical band gap energy was calculated to be 2.95 eV, 2.80 eV, 2.15 eV, 2.35 eV, 2.45 eV, 2.00 eV and 2.25 eV for SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80), respectively. It was expected that the optical band gap energy would decrease as the WO\u003csub\u003e3\u003c/sub\u003e content of the composite film sample increased. The optical band gap energy of the composite film samples ranged from 2.00 eV to 2.95 eV.\u003c/p\u003e \u003cp\u003eThe UV-Vis absorption spectrum of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples is also shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10) film sample has a weak absorption in the UV region (in the range of 250\u0026ndash;400 nm). The intensity of the absorption band increased as the ZnO content of the film sample increased. Since the solar cell generates electricity by absorbing mostly the visible light region of the incoming sunlight, absorption in the UV light range was not expected to have a negative impact on the efficiency of the solar cell. According to the Tauc plot analysis (Fig. S4), the optical band gap energy was estimated to be 2.70 eV, 2.95 eV and 3.20 eV for the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film samples, respectively. The optical band gap of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film sample was widened with an increase in the ZnO content, which might be detrimental to the photocatalytic activity and beneficial to the solar cell efficiency.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003ePhotocatalytic dye degradation efficiency\u003c/h2\u003e \u003cp\u003eWO\u003csub\u003e3\u003c/sub\u003e has been widely studied as a photocatalyst due to its superior properties such as photostability, non-toxicity, chemical and thermal stability. In addition, it exhibits excellent solar radiation absorption due to its favorable band gap [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. However, there is a main problem, limiting the pratical application of WO\u003csub\u003e3\u003c/sub\u003e. The rapid recombination of the photoexcited electrons with holes leads to a low quantum efficiency and photocatalytic dye degradation efficiency. In literature, many attempts have been performed to reduce the recombination rate of the photoinduced charge carriers on the photocatalyts. Coupling WO\u003csub\u003e3\u003c/sub\u003e with another semiconductor can reduce the recombination rate of the mobile charge carriers [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Within the scope of the coupling WO\u003csub\u003e3\u003c/sub\u003e with another semiconductor, WO\u003csub\u003e3\u003c/sub\u003e was combined with SiO\u003csub\u003e2\u003c/sub\u003e in the composite film structure. The photocatalytic degradation of methylene blue might be composed of four steps. When the film sample was exposed to UV light, the valence band electrons were excited to the conduction band to form photoexcited electron-hole pairs (4). The photoinduced charge carriers transferred to the surface of the film sample and reacted with the dye molecules. The surface adsorbed H\u003csub\u003e2\u003c/sub\u003eO molecules might be oxidized by the photogenerated holes to hydroxyl radicals (5) and the dissolved O\u003csub\u003e2\u003c/sub\u003e molecules might be reduced by the photogenerated electrons to superoxide radicals on the surface of the film samples (6). Both of these radicals are highly active and can degrade any organic molecules into simple molecules like H\u003csub\u003e2\u003c/sub\u003eO and CO\u003csub\u003e2\u003c/sub\u003e (7) [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;hv \u0026rarr; e\u003csup\u003e\u0026minus;\u003c/sup\u003e + h\u003csup\u003e+\u003c/sup\u003e (4)\u003c/p\u003e \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;h\u003csup\u003e+\u003c/sup\u003e \u0026rarr; \u0026middot;OH\u0026thinsp;+\u0026thinsp;H\u003csup\u003e+\u003c/sup\u003e (5)\u003c/p\u003e \u003cp\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; \u0026middot;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (6)\u003c/p\u003e \u003cp\u003e\u0026middot;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e + \u0026middot;OH\u0026thinsp;+\u0026thinsp;organic dye \u0026rarr; degradation products (7)\u003c/p\u003e \u003cp\u003eFigure S5 and S6 illustrate UV-Vis absorption spectra of methylene blue in the presence of pure and the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite film samples. The absorption intensity decreased gradually with time under the UVA light irradiation for all film samples. At the end of 240 min of UVA light irradiation, the maximum absorption peak of methylene blue decreased to the lowest value with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) sample, which means that the highest photocatalytic dye degradation was obtained with the specified film sample. The photocatalytic dye degradation efficiency of the as-prepared film samples was calculated using the initial absorbance of the dye solution and the absorbance value of methylene blue solution exposed to the UVA light irradiation. In order to better compare the photocatalytic activity of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite films, all dye degradation efficiency values were plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. After 240 min of the UVA light irradiation, the photocatalytic dye degradation efficiency was 25.2%, 46.1%, 53.5%, 68.8%, 75.2%, 84.6%, and 58.2% for the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80) films, respectively. The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample exhibited the highest photocatalytic activity. When compared with pure SiO\u003csub\u003e2\u003c/sub\u003e and pure WO\u003csub\u003e3\u003c/sub\u003e film samples, there was a significant enhancement in the photocatalytic activity of the composite film samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Pure SiO\u003csub\u003e2\u003c/sub\u003e and pure WO\u003csub\u003e3\u003c/sub\u003e film samples were able to degrade 5.6% and 24.0% of methylene blue, respectively, after 240 minutes of the UVA light irradiation. According to Hu and his coworkers (2012), the interaction between SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e in the composite structure might led to the formation of the oxygen vacancy. The oxygen vacancy led to the formation of a defect state between the conduction and valence bands of WO\u003csub\u003e3\u003c/sub\u003e. The specified defect state might act as the hole trap, suppressing the recombination rate of the photogenerated electron-hole pairs [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Any effect that decreases the recombination rate of the photoinduced electron-hole pairs or increases the number of charge carriers positively affects the photocatalytic efficiency. In literature, according to Li and his coworkers (2014), the SiO\u003csub\u003e2\u003c/sub\u003e surface was rich in the hydroxyl radicals in the aqueous medium. The increase in the number of the hydroxyl radicals on the SiO\u003csub\u003e2\u003c/sub\u003e surface improved the ability of the composite sample to retain the absorbed water, which might result in an increase in the reaction rate between the dye molecules and WO\u003csub\u003e3\u003c/sub\u003e. In addition, SiO\u003csub\u003e2\u003c/sub\u003e had a high tendency to trap the photoexcited electrons in its conduction band, suppressing the recombination rate of the photogenerated electron-hole pairs [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The electron trapping ability of SiO\u003csub\u003e2\u003c/sub\u003e might also be the reason for the significant enhancement in the photoactivity of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite film sample. The trapping of the photoexcited electrons of WO\u003csub\u003e3\u003c/sub\u003e on the conduction band of SiO\u003csub\u003e2\u003c/sub\u003e might contribute to the effective separation of the mobile charge carrier, which are necessary to form the active radicals responsible for the degradation of the organic dye molecules. The weight ratio of SiO\u003csub\u003e2\u003c/sub\u003e to WO\u003csub\u003e3\u003c/sub\u003e was critical in terms of the photocatalytic activity. The weight ratio of the composite constituents might affect the contact effectiveness between SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e particles. The excess of any of the composite components might reduce the contact between the SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e particles. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the optimum composition (SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70)) might provide the effective contact between SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e particles. Increasing or decreasing the WO\u003csub\u003e3\u003c/sub\u003e content of the composite from the optimum value might reduce the contact interface between SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e particles, suppressing the effective transfer of the photoinduced electron-hole pairs between the composite constituents. Hence, many photoinduced charge carriers might recombine on SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e, decreasing the photocatalytic dye degradation efficiency [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to Jourshabani and Lee (2021), the bottom energy state of the conduction band for WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e were equivalent to -0.66 eV and \u0026minus;\u0026thinsp;0.56 eV (vs NHE), respectively. The top energy state of the valence band for WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e were equivalent to 2.26 eV and 3.65 eV (vs NHE), respectively. Coupling WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e in the composite structure affected the charge transfer by different pathways, leading to an improvement in the photocatalytic activity [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. The contact points between SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e might have a significant role in suppressing the recombination of the photoexcited electron-hole pairs, which was also confirmed by Jourshabani and Lee (2021) [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite could form hydroxyl radicals from surface adsorbed water molecules because the composite could provide sufficient driving force for the formation of the oxidation reaction of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/\u0026bull;OH (1.99 eV vs. NHE). In addition, the composite sample could form superoxide radicals from surface adsorbed oxygen molecules because the conduction band position of both WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e could overcome the thermodynamic barrier of the reduction reaction of O\u003csub\u003e2\u003c/sub\u003e/\u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (-0.33 eV vs NHE) [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Because of the potential differences in the band energy levels of SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e, the photoexcited electrons of WO\u003csub\u003e3\u003c/sub\u003e could transfer to the conduction band SiO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The opposite was true for the photoexcited holes formed on SiO\u003csub\u003e2\u003c/sub\u003e. The photogenerated holes of SiO\u003csub\u003e2\u003c/sub\u003e could transfer to the valence band of WO\u003csub\u003e3\u003c/sub\u003e. Thus, the photoinduced electron-hole pairs might be effectively separated. The superoxide radicals might be generated directly or indirectly by the photoinduced electrons of SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e. Similarly, the hydroxyl radicals might be formed directly or indirectly by the photoinduced holes of WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Langmuir-Hinshelwood model was utilized to analyze the reaction rate of heterogeneous photocatalysis for the degradation of methylene blue on the film samples. The Langmuir-Hinshelwood model formula is given below [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eln(C\u003csub\u003e0\u003c/sub\u003e/C)\u0026thinsp;=\u0026thinsp;kt (8)\u003c/p\u003e \u003cp\u003ewhere C\u003csub\u003e0\u003c/sub\u003e and C are the concentration of methylene blue solution before and after the UV light irradiation, respectively. In addition, k is the apparent pseudo-first-order reaction rate constant, which was obtained from the plot of ln(C/C\u003csub\u003e0\u003c/sub\u003e) vs. t (Fig. S7). Fig. S7 confirmed that the pseudo-first-order was followed by the photocatalytic dye degradation reactions in the presence of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film samples. The reaction rate constant values were compared on Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The highest reaction rate constant was obtained with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample. Compared to pure SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e film samples, a significant increase in the reaction rate of the photocatalytic degradation of methylene blue was obtained with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe photocatalytic dye degradation rate on the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ek (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.7897\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9913\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9088\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0059\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.7879\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0065\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9369\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0078\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9905\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0038\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9970\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe photocatalytic dye degradation rate on pure SiO\u003csub\u003e2\u003c/sub\u003e, pure WO\u003csub\u003e3\u003c/sub\u003e and ZnO film samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ek (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure SiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9705\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure WO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0012\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9833\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePure ZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0163\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.2326\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTo enhance the photocatalytic dye degradation efficiency of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite system, it was also coupled with a well-known photocatalyst ZnO. Since the highest photocatalytic activity was obtained with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample, this composition was utilized to prepare the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO composite films. Fig. S8 shows the absorption spectrum methylene blue in the presence of SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples. A decrease in the absorption spectrum intensity was observed with time under the UVA light irradiation. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e illustrates the percentage of the photocatalytic degradation of the model dye in the aqueous solution using the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples. Compared to the optimum SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite film sample (SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70)), the photocatalytic degradation percentage of methylene blue was enhanced on the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film sample. Combining the optimum SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composition with ZnO seemed to be effective in terms of the photocatalytic activity. The maximum dye degradation percentage for SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) was obtained as 86.1%, 86.3% and 91.6%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure S9 illustrates the kinetics of the photocatalytic degradation of the model dye. The degradation kinetics seemed to fit to the pseudo-first-order reaction model (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The reaction rate constant value for SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) were 0.0088, 0.0088 and 0.0110 min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. The reaction rate constant values revealed that the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO composites were more active to degrade the dye molecules in the aquatic environment under the UVA irradiation. With the contribution of ZnO to the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite system, the reaction rate was increased by about 1.4 times. Due to its high photocatalytic activity, ZnO might enhance the photocatalytic dye degradation efficiency of the resulting composite system.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eReaction rate constant values of the model dye degradation on the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films under the UVA light irradiation\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ek (min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9705\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0088\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9939\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.0088\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.9914\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAccording to Lu and his coworkers (2016), the bottom energy state of the conduction band for ZnO was equivalent to -0.26 eV (vs NHE) and the top energy state of the valence band for ZnO was equivalent to 2.85 eV (vs NHE) [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. When ZnO was combined with SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e, the conduction band potential of ZnO was more positive than that of SiO\u003csub\u003e2\u003c/sub\u003e and WO\u003csub\u003e3\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). In addition, the valence band potential of ZnO was more positive than that of WO\u003csub\u003e3\u003c/sub\u003e. Thus, the photoinduced electrons of both WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e might transfer to the conduction band of ZnO. Also, the photoinduced holes of ZnO might transfer to the valence band of WO\u003csub\u003e3\u003c/sub\u003e. Hence, the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO heterostructure might effectively separate the photogenerated mobile charge carriers on the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e composite, further improving the photocatalytic dye degradation efficiency. The effectively separated electron-hole pairs could migrate to the photocatalyst surface to form the active radicals necessary to degrade the methylene blue molecules. ZnO in the composite structure could also form the hydroxyl radical from the surface adsorbed water molecules because the redox potential of the couple OH\u003csup\u003e\u0026minus;\u003c/sup\u003e/\u0026bull;OH, which is 1.99 eV vs. NHE, was more negative than the valence band edge potential of ZnO. According to the redox potentials of the couple O\u003csub\u003e2\u003c/sub\u003e/\u0026middot;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (-0.33 eV vs. NHE), the surface adsorbed O\u003csub\u003e2\u003c/sub\u003e molecules could not be reduced by the photogenerated electrons of ZnO to superoxide anion radicals (\u0026middot;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWithin the scope of the optimization study, the effect of the number of the dip-coating cycle on the photocatalytic activity was also studied. According Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) (1-fold coating), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) (2-fold coating), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) (3-fold coating) film samples exhibited the dye degradation efficiency of 84.6%, 86.6% and 81.1%, respectively, after 240 min. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e also illustrates the photocatalytic degradation of the model dye on SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (1-fold coating), SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (2-fold coating) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) (3-fold coating) film samples, respectively. When the model dye was irradiated on the 1-fold coated SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30), 2-fold coated SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) and 3-fold coated SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films samples, the degradation of methylene blue reached the maximum of 91.6%, 91.0% and 90.0%, respectively, after 240 min of the UVA light irradiation. It was observed that the degradation of the model dye was weakly dependent on the number of the dip-coating cycle.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eSolar Cell Efficiency\u003c/h2\u003e \u003cp\u003eGlass slides coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e or SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples were used to measure the effect of the coated film on the real solar cell. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e illustrates the variation of the obtained voltage with the current by an uncoated and coated solar cells. The fill factor (FF) and the efficiency of the uncoated (standard) solar cell and coated solar cells were summarized on Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. In general, relatively higher solar cell efficiency was achieved with the composite films including high SiO\u003csub\u003e2\u003c/sub\u003e content. The solar cell efficiency experiment was performed under a solar light simulator. Due to its wide optical band gap, the SiO\u003csub\u003e2\u003c/sub\u003e film could transmit most of the incident light to the absorber layer of the solar cell. The WO\u003csub\u003e3\u003c/sub\u003e film coating, which has a narrower optical band gap than that of SiO\u003csub\u003e2\u003c/sub\u003e, could reduce the efficiency of the solar cell by absorbing more of the incoming light. The light transmittance spectroscopy supported this idea. The composite film samples with high SiO\u003csub\u003e2\u003c/sub\u003e content exhibited high transmittance in both UV and visible light regions. Compared to the uncoated solar cell (standard), higher efficiency was achieved by the solar cell including the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50) film samples, respectively. The reason for the improvement in the solar cell efficiency might be the reflective feature of the specified film coatings. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e also illustrates the voltage-current characteristics of the solar cell coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples. To prepare the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film samples, the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film sample was utilized and coupled with ZnO in varying compositions. Compared to the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film coating, the solar cell efficiency slightly increased. The wide optical band gap and the anti-reflective feature of ZnO might be the possible reason for the improvement in the solar cell efficiency. When compared with the uncoated solar cell (standard), approximately the same efficiency value was obtained with the solar cell coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20) films, respectively. As the ZnO content of the SiO\u003csub\u003e2\u003c/sub\u003e-WO\u003csub\u003e3\u003c/sub\u003e/ZnO films increased, the solar cell efficiency slightly decreased. To analyze the individual effect of the composite phases on the solar cell efficiency, the voltage-current characteristics of the solar cell coated with pure SiO\u003csub\u003e2\u003c/sub\u003e, pure WO\u003csub\u003e3\u003c/sub\u003e and pure ZnO films were also analyzed and their results were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. When compared with the standard solar cell, slightly higher and slightly lower efficiencies were achieved by the solar cell coated with pure SiO\u003csub\u003e2\u003c/sub\u003e film and pure ZnO film, respectively. On the other hand, pure WO\u003csub\u003e3\u003c/sub\u003e film significantly reduced the efficiency of the standard cell (from 5.51 to 2.69).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFill factor (FF) is one of the important parameters to determine the efficiency of a solar system. To get the maximum possible efficiency from a solar module, FF should be maximum and its value should approach one [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The fill factor, the ratio of the theoretical power to the maximum power, can be calculated by using the following relation (9):\u003c/p\u003e \u003cp\u003eFF\u0026thinsp;=\u0026thinsp;V\u003csub\u003eMP\u003c/sub\u003e I\u003csub\u003eMP\u003c/sub\u003e / V\u003csub\u003eOC\u003c/sub\u003e I\u003csub\u003eSC\u003c/sub\u003e (9)\u003c/p\u003e \u003cp\u003ewhere V\u003csub\u003eOC\u003c/sub\u003e is the open circuit voltage, I\u003csub\u003eSC\u003c/sub\u003e is the short circuit current, V\u003csub\u003eMP\u003c/sub\u003e is the voltage value at the maximum power point and I\u003csub\u003eMP\u003c/sub\u003e is the current at the maximum power point [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The fill factor is known as a measure of the quality of a solar cell. Among the solar cells coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e films, only the solar cell coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80) film had a slightly lower FF value than the standard solar cell. Among the solar cells coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films, only the solar cell coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film exhibited a slightly lower FF value compared to the standard solar cell (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The calculated FF values showed that the prepared film samples could be applied to the cover glass of the real photovoltaic system.\u003c/p\u003e \u003cp\u003eWithin the scope of the optimization study, the effect of the number of the dip coating cycle on the solar cell efficiency was also studied (Fig. S10). According to Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, as the number of the dip-coating cycle increased, the efficiency of the solar cell coated with SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO films slightly decreased. Maintaining or, if possible, increasing the efficiency of the solar cell is important for the applicability of the self-cleaning film layer on the solar cell. Therefore, increasing the number of the dip-coating cycle was useless in terms of the efficiency of the solar cell.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEfficiency of the uncoated (standard) and coated solar cells\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003em\u003c/sub\u003e (V)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eI\u003csub\u003em\u003c/sub\u003e (A)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eV\u003csub\u003eoc\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eI\u003csub\u003esc\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eF.F\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eA (m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eP\u003csub\u003eout\u003c/sub\u003e (W/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eP\u003csub\u003ein\u003c/sub\u003e (W/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eɳ (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStandard\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.224\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e55.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.315\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.473\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e56.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.315\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.132\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.471\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.204\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.433\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e51.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.207\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.104\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.299\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.152\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.474\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e26.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e2.69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(80/20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.289\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.434\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.227\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0,440\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e54.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(70/30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.306\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.214\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.476\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e56.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.62\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(60/40)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0,307\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,140\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.461\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e53.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(50/50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.292\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.161\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.421\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e58.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(40/60)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.261\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.195\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e41.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e4.18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.266\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.119\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.385\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.175\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.469\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e39.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(20/80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.264\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.129\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.419\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.197\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e42.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e4.26\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(90/10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.302\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.145\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.454\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.218\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e54.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(80/20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.309\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.142\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.437\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.207\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.485\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e54.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.290\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.142\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e51.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of the number of the dip-coating cycle on the efficiency of the solar cell coated with SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV\u003csub\u003eMP\u003c/sub\u003e (V)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eI\u003csub\u003eMP\u003c/sub\u003e (A)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eV\u003csub\u003eoc\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eI\u003csub\u003esc\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eF.F\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eA (m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eP\u003csub\u003eout\u003c/sub\u003e (W/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eP\u003csub\u003ein\u003c/sub\u003e (W/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eɳ (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStandard\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.147\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.224\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e55.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) 1-fold\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.266\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.119\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.385\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.175\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.469\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e39.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) 2-fold\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.246\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.370\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.167\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.429\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e33.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) 3-fold\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.198\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.097\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.316\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.148\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.411\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e24.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e2.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u0026minus;\u003c/sub\u003eWO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) 1-fold\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.290\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.142\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e51.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e5.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u0026minus;\u003c/sub\u003eWO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) 2-fold\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.262\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.119\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.393\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.441\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e38.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u0026minus;\u003c/sub\u003eWO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) 3-fold\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.124\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.361\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.477\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.0008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e38.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e3.88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eWater angle measurements\u003c/h2\u003e \u003cp\u003eOne of the most conventional techniques to investigate the photocatalytic self-cleaning feature of the film samples is the dye technique [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In the dye technique, the model dye is considered as contamination on the film and the photocatalytic degradation of the dye molecules under the UV light radiation is studied to reveal the self-cleaning feature of the film coatings [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. According to the photocatalytic dye degradation experiments, the prepared film samples could degrade the model dye adsorbed on itself under the UVA light irradiation. Hence, methylene blue as the model dye could be decomposed to water and carbon dioxide. The photocatalytic degradation rate of the methylene blue could be measured by analyzing the rate of water formation through the contact angle measurement [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The formation of water molecules on the film surface could change the surface energy, leading to a reduction in the water contact angle. The photocatalytic activity of the film samples was also studied using the dye technique. The water contact angle measurement was performed on the film samples adsorbed by the methylene blue and exposed the UVA light irradiation. Figure\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e illustrate the change of the water contact angle with the irradiation time, and Fig. S11 and S12 illustrate the images of the water droplets on the film samples. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e, the water contact angle exhibited a decrease with the irradiation time. The water contact angle of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) film and the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) film decreased from 45.1\u0026deg;, 64.1\u0026deg; to 29.2\u0026deg;, 45.4\u0026deg;, respectively, after 240 min of the UVA light irradiation. The water contact angle measurement revealed that the composite film samples were able to degrade the model dye adsorbed on itself with time and the film samples exhibited photocatalytic activity. Both the photocatalytic dye degradation and the water contact angle measurements verified the high photocatalytic activity of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e(30/70) and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO(70/30) films.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe objective of this study was to coat the top layer of the solar cell with composite (SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO) films, which had the ability of self-cleaning under the UVA light irradiation. The film coatings provided the self-cleaning process through the photocatalytic activity and the photoinduced hydrophilicity. Within this scope, WO\u003csub\u003e3\u003c/sub\u003e was compounded with a highly transparent semiconductor SiO\u003csub\u003e2\u003c/sub\u003e, minimizing the the transmission loss on the solar cell. ZnO was also added into the film structure to provide an enhanced photocatalytic activity. The SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film coatings exhibited high visible light transmittance and photocatalytic activity under the UVA light irradiation. The self-cleaning performance of the prepared film coatings was also so high that the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film could degrade more than 90% of the model contaminant on itself within 240 min of the UVA light irradiation. The hydrophilicty of the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film coated with the model contaminant increased with the irradiation, exhibiting the photocatalytic degaradtion efficiency of the prepared films. The current-voltage measurement of the solar cell coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film did not exhibit any significant loss in efficiency. The results of the study revealed that the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film can be applied as a comercial product on the PV panel surfaces against the accumulation of any kinds of pollution, resulting in the reduction of the PV efficiency.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor informations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnkara University, Engineering Faculty, Energy Systems Engineering, Ankara, 06830, TURKEY\u003c/p\u003e\n\u003cp\u003eOzcan Koysuren, Savas Yaglikci, Bilge Tuncel\u003c/p\u003e\n\u003cp\u003ePolytechnic University of Tirana, Faculty of Mechanical Engineering, Department of Production and Management, Tirana, 1001, ALBANIA\u003c/p\u003e\n\u003cp\u003eKlodian Dhoska, Irida Markja,\u003c/p\u003e\n\u003cp\u003eKirsehir Ahi Evran University, Faculty of Engineering and Architecture, Department of Environmental Engineering, Kirsehir, 40100, TURKEY\u003c/p\u003e\n\u003cp\u003eHafize Nagehan Koysuren\u003c/p\u003e\n\u003cp\u003ePolytechnic University of Tirana, Faculty of Mechanical Engineering, Energy Department, Tirana, 1001, ALBANIA\u003c/p\u003e\n\u003cp\u003eElena Bebi\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorresponding Author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence to Ozcan Koysuren or Klodian Dhoska\u003c/p\u003e\n\u003cp\u003eStatements \u0026amp; Declarations\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research has been supported by The Scientific and Technological Research Council of Turkey (T\u0026Uuml;BİTAK) and National Agency of Scientific Research and Innovation (NASRI) with the Project Number 122N383.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by all authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEstekhraji SAZ, Amiri S (2017) Sol-gel preparation and characterization of antibacterial and self-cleaning hybrid nanocomposite coatings. J Coat Technol Res 14(6):1335\u0026ndash;1343\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhorshidi ZG, Jallab M, Moghbelli E, Goudarzi A, Ghaffari M (2021) Photocatalytic Analysis of a Hydrophilic Acrylic Coating/Zinc Oxide Nanocomposite on Glass Substrate. Polym-Plast Technol Mater 60(11):1220\u0026ndash;1232\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePakdel E, Zhao H, Wang JF, Tang B, Varley RJ, Wang XG (2021) Superhydrophobic and photocatalytic self-cleaning cotton fabric using flower-like N-doped TiO2/PDMS coating. Cellulose 28(13):8807\u0026ndash;8820\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatte J, Van Zele M, De Buysser K, Van Driessche I (2018) Recent Advances in Low-Temperature Deposition Methods of Transparent, Photocatalytic TiO2 Coatings on Polymers. Coatings 8(4):131\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao Q, Wu XM, Cai LG (2021) Facial synthesis of K0.3WO3/Ag nanocomposites for self-cleaning energy efficient window coatings. J Alloys Compd 856:157069\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuevano-Hipolito E, Torres-Martinez LM, Cantu-Castro LVF (2019) Self-cleaning coatings based on fly ash and bismuth-photocatalysts: Bi2O3, Bi2O2CO3, BiOI, BiVO4, BiPO4. Constr Build Mater 220:206\u0026ndash;213\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVulic T, Rudic O, Vucetic S, Lazar D, Ranogajec J (2015) Photocatalytic activity and stability of TiO2/ZnAl layered double hydroxide based coatings on mortar substrates. Cem Concr Compos 58:50\u0026ndash;58\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNoh HN, Myong SY (2014) Antireflective coating using a WO3-TiO2 nanoparticle photocatalytic composition for high efficiency thin-film Si photovoltaic modules. Sol Energy Mater Sol Cells 121:108\u0026ndash;113\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSoklic A, Tasbihi M, Kete M, Stangar UL (2015) Deposition and possible influence of a self-cleaning thin TiO2/SiO2 film on a photovoltaic module efficiency. Catal Today 252:54\u0026ndash;60\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHosseini MS, Ebratkhahan M, Shayegan Z, Niaei A, Salari D, Rostami A, Raeisipour J (2020) Investigation of the effective operational parameters of self-cleaning glass surface coating to improve methylene blue removal efficiency; application in solar cells. Sol Energy 207:398\u0026ndash;408\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJovanov V, Zecevic V, Vulic T, Ranogajec J, Fidanchevska E (2018) Preparation and characterization of protective self-cleaning TiO2/kaolin composite coating. Mater Constr 68(331):163\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRudakova AV, Emeline AV (2021) Photoinduced Hydrophilicity of Surfaces of Thin Films. Colloid J 83(1):20\u0026ndash;48\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSyafiq A, Pandey AK, Adzman NN, Abd Rahim N (2018) Advances in approaches and methods for self-cleaning of solar photovoltaic panels. Sol Energy 162:597\u0026ndash;619\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThwala MM, Dlamini LN (2020) Photocatalytic reduction of Cr(VI) using Mg-doped WO3 nanoparticles. Environ Technol 41(17):2277\u0026ndash;2292\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNagarjuna R, Challagulla S, Sahu P, Roy S, Ganesan R (2017) Polymerizable sol-gel synthesis of nano-crystalline WO3 and its photocatalytic Cr(VI) reduction under visible light. Adv Powder Technol 28(12):3265\u0026ndash;3273\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAi L, Jia D, Guo N, Xu M, Zhang S, Wang L, Jia L (2020) Cl-doped Bi2S3 homojunction nanorods with rich-defects for collaboratively boosting photocatalytic reduction performance. Appl Surf Sci 529:147002\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou G, Long L, Wang P, Hu Y, Zhang Q, Liu C (2020) Designing CuO/ZnO nanoforest device toward optimal photocatalytic performance through structure and facet engineering. Mater Lett 273:127907\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarvalho LM, Soares AF, Lima MS, Cruz-Filho JF, Dantas TCM, Luz GE (2021) 2,4-Dichlorophenoxyacetic acid (2,4-D) photodegradation on WO3-TiO2-SBA-15 nanostructured composite. Environ Sci Pollut Res 28(7): 7774\u0026ndash;7785\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi J, Du X, Yao L, Zhang Y (2014) Synthesis of SnS2/WO3 nanocomposite with enhanced photocatalytic activity. Mater Lett 121:44\u0026ndash;46[\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShi J, Liao R, Jia R, Liu Y, Wu D, Chang S, Zhang N, Gao G, Wang X, Hu D, Wu K (2023) A novel combustion drying synthesis route of 3D WO3\u0026ndash;SiO2 composite aerogels for enhanced adsorption and visible light photocatalytic activity. J Non-Cryst Solids 609:122259\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang J, Guo Y, Xiong Y, Zhou D, Dong S (2017) An environmentally friendly Z-scheme WO3/CDots/CdS heterostructure with remarkable photocatalytic activity and anti-photocorrosion performance. J Catal 356:1\u0026ndash;13\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDozzi MV, Marzorati S, Longhi M, Coduri M, Artiglia L, Selli E (2016) Photocatalytic activity of TiO2-WO3 mixed oxides in relation to electron transfer efficiency. Appl Catal B-Environ 186:157\u0026ndash;165\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAli AM, Ismail AA, Bouzid H, Harraz FA (2014) Sol\u0026ndash;gel synthesis of ZnO\u0026ndash;SiO2 thin films: impact of ZnO contents on its photonic efficiency. J Sol-Gel Sci Technol 71:224\u0026ndash;233\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYao L, He JH (2014) Facile dip-coating approach to fabrication of mechanically robust hybrid thin films with high transmittance and durable superhydrophilicity. J mater Chem A 2(19):6994\u0026ndash;7003\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi Y, Yang K, Xia B, Yang B, Yan L, He M, Yan H, Jiang B (2017) Preparation of mechanically stable triple-layer interference broadband antireflective coatings with self-cleaning property by sol\u0026ndash;gel technique. RSC Adv 7, 14660\u0026ndash;14668.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eThilagavathi T, Venugopal D, Marnadu R, Chandrasekaran J, Alshahrani T, Shkir M (2021) An Investigation on Microstructural, Morphological, Optical, Photoluminescence and Photocatalytic Activity of WO(3) for Photocatalysis Applications: An Effect of Annealing. J Inorg Organomet Polym Mater 31(3):1217\u0026ndash;1230\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang M, Kim EJ, Chung JS, Shin EW, Hahn SH, Lee KE, Park C (2006) Influence of annealing temperature on the structural and optical properties of sol\u0026ndash;gel prepared ZnO thin films. Phys Status Solidi A-Appl Mat 203:2418\u0026ndash;2424\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRen YF, Li WT, Cao ZH, Jiao YP, Xu JJ, Liu P, Li S, Li X (2020) Robust TiO2 nanorods-SiO2 core-shell coating with high-performance self-cleaning properties under visible light. Appl Surf Sci 509:145377\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaravanan S, Dubey D, Raghvendra S (2020) Synthesis of SiO2 Nanoparticles by Sol-Gel Method and Their Optical and Structural Properties. Rom J Inf Sci Technol 23:105\u0026ndash;112\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGui-Long X, Changyun D, Yun L, Pi-Hui P, Jian H Zhuoru Y (2011) Preparation and characterization of Raspberry-like SiO2 particles by the sol-gel method. Nanomater Nanotechnol 1:21\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoran F, \u0026Ccedil;etinkaya S (2017) Synthesis, Characterization and Sensing Behavior of WO₃ Nanocrystalline Powder for Toluene Vapor. Acta Phys Pol A 132(3):572\u0026ndash;573\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAksoy S, Caglar Y (2019) Synthesis of Mn doped ZnO nanopowders by MW-HTS and its structural, morphological and optical characteristics. J Alloys Compd 781:929\u0026ndash;935\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJayarambabu N, Kumari BS, Rao KV, Prabhu YT (2014) Germination and growth characteristics of mungbean seeds (Vigna radiata L.) affected by synthesized zinc oxide nanoparticles. Int J Curr Eng Technol 4(5):3411\u0026ndash;3416\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSakthisabarimoorthi A, Dhas SMB, Jose M (2020) Study on optical nonlinearity of Au@ SiO2 composite nanoparticles towards photonic applications. Mater Chem Phys 240:122154\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJerold Antony A, Mary Jelastin Kala S, Joel C, Biju Bennie R, Vivetha S (2022) Structural, optical, and magnetic properties of pristine and Cr doped WO3 nanoparticles. Inorg Nano-Met Chem 52(7):951\u0026ndash;960\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi X, He S, Liu X, Jin J, Meng H (2019) Polymer-assisted freeze-drying synthesis of Ag-doped ZnO nanoparticles with enhanced photocatalytic activity. Ceram Int 45(1):494\u0026ndash;502\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMuljani S, Wahyudi B, Sumada K (2016) Potassium silicate foliar fertilizer grade from geothermal sludge and pyrophyllite. In MATEC Web of Conferences (Vol.\u0026nbsp;58, p.\u0026nbsp;01021). EDP Sciences\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChahi M, Alc\u0026aacute;ntara SP, Bouhekka A, Sib JD, Sanchez G, Chahed L (2020) The enhancement of near infrared light trapping in solar cells with backside crystalline silicon gratings: Realization and characterization investigation, Optik 200:163142\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFarhadian M, Sangpour P, Hosseinzadeh G (2015) Morphology dependent photocatalytic activity of WO3 nanostructures. J Energy Chem 24(2):171\u0026ndash;177\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang SM, Yan XX, Deng DM, He HB, Lei YY, Shen X, Luo LQ (2019) Controllable synthesis and enhanced photocatalytic activity of B-TiO2 nanospheres. Micro Nano Lett 14(7):740\u0026ndash;743\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu T, Li JY, Chang MQ, Song YH, Sun Q, Wang FK, Zou HF, Shi Z (2021) Photoluminescence properties and photocatalytic activities of SiO2@TiO2:Sm3\u0026thinsp;+\u0026thinsp;nanomaterials. J Phys Chem 149:109775\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu SZ, Li FY, Fan ZP (2012) Preparation of SiO2-Coated TiO2 Composite Materials with Enhanced Photocatalytic Activity Under UV Light. Bull Korean Chem Soc 33(6):1895\u0026ndash;1899\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJourshabani M, Lee BK (2021) Unmasking the Role of an Amorphous/Amorphous Interface and a Crystalline/Amorphous Interface in the Transition of Charge Carriers on the CN/SiO2/WO3 Photocatalyst. ACS Appl Mater Interfaces 13(27):31785\u0026ndash;31798\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHamed NKA, Ahmad MK, Hairom NHH, Faridah AB, Mamat MH, Mohamed A, Suriani AB, Soon CF, Fazli FIM, Mokhtar SM (2022) Photocatalytic degradation of methylene blue by flowerlike rutile-phase TiO2 film grown via hydrothermal method. J Sol-Gel Sci Technol 102(3):637\u0026ndash;648\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLu C, Zhimin BZ, Qin C, Dai L, Zhu A (2016) Facile fabrication of heterostructured cubic-CuFe2O4/ZnO nanofibers (c-CFZs) with enhanced visible-light photocatalytic activity and magnetic separation. RSC Adv 6:110155\u0026ndash;110163\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma DK, Purohit G (2014) Analysis of the effect of fill factor on the efficiency of solar PV system for improved design of MPPT. In 6th world conference on photo voltaic energy conversion\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAuthor informations\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnkara University, Engineering Faculty, Energy Systems Engineering, Ankara, 06830, TURKEY\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOzcan Koysuren, Savas Yaglikci, Bilge Tuncel\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolytechnic University of Tirana, Faculty of Mechanical Engineering, Department of Production and Management, Tirana, 1001, ALBANIA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKlodian Dhoska, Irida Markja,\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKirsehir Ahi Evran University, Faculty of Engineering and Architecture, Department of Environmental Engineering, Kirsehir, 40100, TURKEY\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHafize Nagehan Koysuren\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolytechnic University of Tirana, Faculty of Mechanical Engineering, Energy Department, Tirana, 1001, ALBANIA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eElena Bebi\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCorresponding Author\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCorrespondence to Ozcan Koysuren or Klodian Dhoska\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStatements \u0026amp; Declarations\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-sol-gel-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jsst","sideBox":"Learn more about [Journal of Sol-Gel Science and Technology](https://www.springer.com/journal/10971)","snPcode":"10971","submissionUrl":"https://submission.springernature.com/new-submission/10971/3","title":"Journal of Sol-Gel Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Self-cleaning coatings, solar cell, photocatalytic activity, hydrophilic coatings","lastPublishedDoi":"10.21203/rs.3.rs-3704926/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3704926/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe accumulation of pollution and any kinds of contamination on the glass cover of the solar cell affects the efficiency of the photovoltaic (PV) systems. The contamination on the glass cover can absorb and reflect a certain part of the sunlight irradiation, which can decrease the intensity of the light coming in through the glass cover. With the study, it was planned to develop self-cleaning coatings for the PV systems. It was aimed to prevent or reduce the contamination-induced efficiency loss of the existing PV systems. In the scope of the project, SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO composites were coated from their solutions on the glass substrates using a dip-coating technique. WO\u003csub\u003e3\u003c/sub\u003e was selected as a photocatalyst semiconductor. Under the UV light irradiation, WO\u003csub\u003e3\u003c/sub\u003e could absorb the photons of the UV light, generating the photoinduced charge carriers. The photoexcited charge carriers provide both the photoinduced hydrophilicity on the surface of the coating and the photocatalytic degradation of the organic contaminants accumulated on the surface of the coating, which allows water droplets to spread and flow on the surface of the cover glass to remove the contaminations. However, the recombination rate of the photoexcited charge carriers on the WO\u003csub\u003e3\u003c/sub\u003e film was high. In order to suppress the recombination of the photoinduced charge carriers, WO\u003csub\u003e3\u003c/sub\u003e was coupled with SiO\u003csub\u003e2\u003c/sub\u003e and ZnO. Both of these semiconductors improved the photocatalytic activity of the WO\u003csub\u003e3\u003c/sub\u003e film. Although SiO\u003csub\u003e2\u003c/sub\u003e has superior features in terms of the light transmission, it was not very effective under UV light as a photocatalyst alone. The widely preferred photocatalyst ZnO was added into the composite film structure to enhance the photocatalytic activity. The self-cleaning mechanism of the film coatings on a solar cell was investigated through the photocatalytic dye removal efficiency on the as-prepared film samples. There was a slight decrease in the light transparency and the solar cell efficiency because of the WO\u003csub\u003e3\u003c/sub\u003e content of the composite film. On the other hand, coupling the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e film with ZnO enhanced the photocatalytic activity, and it suppressed the reduction effect of the WO\u003csub\u003e3\u003c/sub\u003e phase on both the light transparency and the solar cell efficiency. The photocatalytic dye removal efficiency was increased to over 90% after 240 min of UVA light irradiation. In addition, the solar cell coated with the SiO\u003csub\u003e2\u003c/sub\u003e/WO\u003csub\u003e3\u003c/sub\u003e/ZnO film provided almost the same solar cell efficiency as the uncoated solar cell. The water contact angle measurement also exhibited the photocatalytic degradation of the model contamination on the glass cover of the solar cell under the UVA light irradiation.\u003c/p\u003e","manuscriptTitle":"SiO2 /WO3 /ZnO Based Self-cleaning Coatings for Solar Cells","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-12-07 15:22:37","doi":"10.21203/rs.3.rs-3704926/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-01-31T14:57:39+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-26T12:48:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"2d06e44c-f488-4a0f-9ac7-72cb6312e78f","date":"2024-01-14T21:56:19+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-08T14:02:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"b4e8e3f3-6b48-4076-92a7-9cb8a609a004","date":"2024-01-06T03:11:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"fac8d634-5975-43a0-9369-8394468b30cb","date":"2023-12-29T07:22:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-12-12T17:02:57+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-12-05T11:08:57+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-12-05T11:08:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Sol-Gel Science and Technology","date":"2023-12-04T08:41:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-sol-gel-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jsst","sideBox":"Learn more about [Journal of Sol-Gel Science and Technology](https://www.springer.com/journal/10971)","snPcode":"10971","submissionUrl":"https://submission.springernature.com/new-submission/10971/3","title":"Journal of Sol-Gel Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"457fa9ba-a204-41c4-a1e9-319259af53ae","owner":[],"postedDate":"December 7th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-03-11T15:06:40+00:00","versionOfRecord":{"articleIdentity":"rs-3704926","link":"https://doi.org/10.1007/s10971-024-06351-7","journal":{"identity":"journal-of-sol-gel-science-and-technology","isVorOnly":false,"title":"Journal of Sol-Gel Science and Technology"},"publishedOn":"2024-03-06 15:01:58","publishedOnDateReadable":"March 6th, 2024"},"versionCreatedAt":"2023-12-07 15:22:37","video":"","vorDoi":"10.1007/s10971-024-06351-7","vorDoiUrl":"https://doi.org/10.1007/s10971-024-06351-7","workflowStages":[]},"version":"v1","identity":"rs-3704926","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3704926","identity":"rs-3704926","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}