Strategic Integration of Graphene into Multilayer Photoanode; Enhancing Efficiency of Quasi-Solid-State Dye-Sensitized Solar Cells Under Ambient and Low Irradiance

Strategic Integration of Graphene into Multilayer Photoanode; Enhancing Efficiency of Quasi-Solid-State Dye-Sensitized Solar Cells Under Ambient and Low Irradiance | 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 Strategic Integration of Graphene into Multilayer Photoanode; Enhancing Efficiency of Quasi-Solid-State Dye-Sensitized Solar Cells Under Ambient and Low Irradiance T. M. W. J. Bandara, S. M. S. Gunathilake, G. G. D. M. G. Gamachchi, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4335227/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Sep, 2024 Read the published version in Journal of Applied Electrochemistry → Version 1 posted 10 You are reading this latest preprint version Abstract Graphene is a potential candidate material to boost efficiency in solar cells. The performance of multi-layer TiO 2 photoanode based quasi-solid-state dye-sensitized solar cells (DSSCs) is improved by strategically integrating graphene into the appropriate layer of the photoanode. For this purpose, graphene was synthesized from vein graphite, received directly from the mine site, providing a cost-effective, feasible and new approach to enhance DSSC efficiency. Raman and XRD spectra confirm the successful exfoliation of graphite, forming graphene. Graphene integration into layers was analyzed using SEM images. The cells were constructed using photosensitized spin-coated TiO 2 multilayer photoanode, Pt counter-electrode, and binary salts gel-polymer electrolyte. Appreciable performance improvement was observed when graphene was added to the fourth layer of the photoanode. The quasi-solid-state DSSC without graphene demonstrated 5.50% efficiency, 700 mA open circuit voltage, 11.04 mA cm -2 short circuit current density and 71.2% fill factor under 1000 W m -2 irradiation. In contrast, the DSSC improved by graphene exhibited 6.8% efficiency, 13.4 mA cm -2 short circuit current density, 770 mA open circuit voltage and 66.2% fill factor under 1000 Wm -2 irradiation. Furthermore, the efficiency and fill factor increase were observed when the irradiance decreased. The DSSC exhibited a remarkable efficiency of 9.4% under 67 W m -2 irradiance. Achieving higher efficiency for quasi-soid state configuration without relying on volatile solvent-based electrolytes is another significance of this study. The study uncovers that the strategic incorporation of graphene, synthesized in an economically viable manner, into specific layers of the photoanode significantly enhances the power conversion efficiency in DSSCs. Graphene solar cell Low light Efficiency enhancement Dye solar cells Graphene Multilayer Photoanode Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction One of the biggest challenges in the 21 st century is to replace fossil fuels with renewable and more environmentally friendly energy sources while supplying the ever-increasing energy demand. The development of low-cost and efficient solar cells with emerging technologies is the long-term solution to this energy crisis [ 1 , 2 , 3 ]. Due to the lower production costs and the relatively high-power conversion efficiency (PCE), dye-sensitized solar cells (DSSCs) have received greater attention from researchers during the last decade [ 4 , 5 , 6 ]. DSSCs have attained a maximum power conversion efficiency of 15.0% liquid electrolytes under ambient conditions [ 7 ]. The photoanode in a DSSC plays a key role in absorbing light energy and producing current and voltage through photoexcitation. The photoanode consists of a transparent conductive oxide (TCO) layer coated on a glass substrate. On top of this layer lies the mesoporous nanocrystalline wide-bandgap semiconducting material (TiO 2 ). The power conversion efficiency of a DSSC is basically governed by the properties of the photoanode. A high-performing photoanode should have a large specific surface area for more dye adsorption, faster electron transport, high resistance to photo-corrosion, high electrical conductivity, and excellent interfacial contact between the dye molecules and the electrolyte [ 8 , 9 ]. By integrating highly conductive carbon nanostructures such as graphene, graphene oxide, carbon nanotubes and fullerene into TiO 2 photoelectrode, DSSC performance can be enhanced due to the improved charge transport properties TiO 2 composite electrode. Among these carbon materials, graphene stands out due to its remarkable properties such as excellent optical transmittance, tunable bandgap, high specific surface area, and high mechanical strength. Further, with the addition of graphene or graphene quantum dots, the PCE of DSSCs can be improved through up-conversion and down-conversion [ 10 , 11 , 12 ], broadening the spectral absorption of the photoelectrode [ 13 ] and improving electron mobility. Fang et al. first [ 14 ] reported graphene quantum dot (GQD) assisted dye sensitized TiO 2 photoelectrodes demonstrating an efficiency of 6.10%, making 19.6% enhancement with GQD inclusion. Fan et al. [ 15 ] reported a TiO 2 /graphene nanocomposite-based DSSC with 5.77% efficiency which is a 25% enhancement over graphene-free cell. This efficiency improvement is attributed to reduced electrode-electrolyte interfacial resistance, diminished charge recombination rates, enhanced light scattering, and the enhancement of charge transport resulting from the addition of graphene. Pattarith. K et al. [ 16 ], report higher efficiency of 9.15% for the cell optimized using graphene, benefiting from enhanced dye loading, improved of electronic conductivity, and reduced recombination. For an optimized TiO 2 photoelectrodes with RGO and graphene, Tang. B et al. [ 17 ] achieved a state-of-the-art efficiency of 11.8% for optimized TiO 2 photoelectrodes with reduced graphene oxide (RGO) and graphene. The reported higher efficiency is related to enhanced light scattering and the increased surface area for dye adsorption. The above efficiencies have been reported using problematic liquid electrolytes and ambient 1000 W m -2 irradiance. The performance of a DSSC or any other solar cell mainly depends on the intensity of photon flux /solar irradiation incident to the cell. In nature, sunlight intensity does not remain constant throughout the day or year. Some studies have shown that the efficiency of traditional Si-based solar cells decreases with the decreasing irradiance level [ 18 , 19 ]. Only a few studies have been focused on investigating the performance of quasi-solid state DSSCs as a function of light intensity [ 20 ]. In addition, to our knowledge, there are no reported studies focused on investigating the performance of graphene-incorporated photoanode-based quasi-solid state DSSC. Therefore, it is very important to investigate DSSC performance variation with the light intensity in order to estimate the power generation at different times of the day. In addition to graphene and graphene oxide various other carbon-based materials have also been explored for the improving photoanodes in DSSCs. However, each presents its unique set of advantages and disadvantages. Carbon nanotubes (CNTs) for instance, have gained attention due to exceptional electrical conductivity, high surface area, and tubular structure [ 21 , 22 ]. However, challenges such as CNT aggregation and difficulty of achieving uniform distribution on photoanode may have impacted their effective utilization in DSSCs. Carbon nanofibers (SNFs) are one-dimensional nanostructures similar to CNTs with good electrical conductivity and mechanical strength [ 23 ]. Despite their advantages, challenges in synthesizing and difficulty in proper alignment within the photoanode are considerable drawbacks. Carbon aerogels, a three-dimensional porous carbon structure offers a large surface area for dye adsorption and electron transport [ 24 ]. According to the literature, while relatively higher efficiencies are recorded for graphene added DSSCs compared to control devices, the highest efficiency achieved (15%) by conventional DSSCs has not yet been surpassed. Additionally, the complexity of synthesis and poor stability and scalability issues hindered their application. This field necessitates further research to develop effective strategies for integrating carbon-based materials such as graphene into DSSC photoanodes to address these challenges. By taking above mentioned key factors into account, the present study focuses on systematically incorporating a small amount of graphene into the multi-layer photoanode. Interestingly, in this study the integration of graphene into the 4 th layer of the 6-layer TiO 2 photoanode resulted in enhanced solar cell performance. In addition, one of the challenges of utilizing graphene in solar cells is their high cost. This study presents a low-cost feasible, and novel method for synthesizing graphene using vein graphite received directly from the mine site for incorporation into photoanodes. Another significance of this study is achieving higher efficiency for quasi-soid state configuration without relying on volatile solvent-based electrolytes in the DSSCs. 2. Experimental 2.1 Materials Transparent and conducting FTO substrates having a sheet resistance of 10 Ω cm -2 and ruthenium-based 535-bisTBA (N719) dye sensitizer were purchased from Solaronix SA. Titanium dioxide nanopowders of average particle sizes of 21 nm (P25) and 13 nm (P21) were procured from Evonik, Germany. The starting materials for the preparation of the gel polymer electrolyte; iodine (I 2 ), ethylene carbonate (EC), propylene carbonate (PC), 1-Methyl-3-propylimidazolium iodide (MPII) and 4-tert-butylpyridine (4-TBP) with purity greater than 98%, Tetrahexyl ammonium iodide, lithium iodide and Polyethylene oxide (MW = 4,000,000) were purchased from Sigma Aldrich. Before using, tetrahexyl ammonium iodide, lithium iodide and polyethylene oxide (PEO) were vacuum dried for about 2 h at 50 ℃. 2.2 Preparation of graphene Graphene can be synthesized using various methods for applications [ 25 ]. In this study, the electrolyte solution for the exfoliation was prepared by dissolving 26.14 g of K 2 SO 4 in 300 mL of deionized water (0.5 M). Shiny slippery fibrous (SSF) natural Sri Lankan vein graphite obtained from the Kahatagaha mine site mining site was used as starting material [ 26 ]. Two pieces of vein graphite samples were directly used as the anode and cathode. The separation between the two electrodes was kept at about 3 cm and electrochemical exfoliation of graphite was conducted by applying a 10 V (DC) between the two graphite electrodes for 2 hours. After that, the layer floating on the top of the exfoliated graphite (EG) suspension was collected and filtered using a PTFE membrane filter (0.2 µm pore size). Then, the EG was washed several times with DI water to remove residual salt and it was placed in the oven at 80 °C for 3 h. For further exfoliation, 1 g of electrochemically EG was added to 100 ml of DMF and it was sonicated for 3 hours in order to synthesize graphene as already reported [ 27 ]. After the sonication, the solution was stirred with the help of a magnetic stirrer for 24 hours in order to further minimize the particle size. The resulting solution was then oven-dried and the precipitate was used for the characterization and solar cell fabrication. 2.3 Preparation of graphene added multilayer photoelectrode For the preparation of 1 st and 2 nd layers of TiO 2 photoanode, 0.5 g of TiO 2 nanoparticles with an average particle size of 13 nm (P90 powder) was mixed with 0.1 mol dm -3 HNO 3 for about 30 minutes in an agate mortar with a pestle. In order to prevent the coating of TiO 2 in the area needed for FTO contacts, half of the FTO electrode was masked with scotch tape. Then, the TiO 2 slurry was spin-coated on a well-cleaned FTO substrate of 1 cm ´ 2 cm size at 2300 rpm for 2 minutes. For this purpose, freshly prepared TiO 2 slurry was spread homogeneously on the FTO substrate with the help of a pestle, and spinning commenced immediately after the application of the TiO 2 slurry on the glass substrate, without allowing time for it to dry. Subsequently, the photoelectrode was air dried at ambient conditions for 24 h and then, sintered in air at about 450 ℃ for 30 minutes. For the preparation of the 3 rd layer of the photoelectrode, 0.5 g of TiO 2 nanoparticles of particle size 21 nm (P25) was ground with 0.1 mol dm -3 and the resulting slurry was spin-coated at 1000 rpm for 2 minutes and followed by sintering at 450 ℃. The 4 th , 5 th and 6 th TiO 2 layers were prepared following the spin coating and sintering process used for the 3 rd layer preparation, except that, 0.1 g of PEO (4,000,000 molar weight) and a few drops of Titron X 100 (surfactant) were added to the TiO 2 slurry and well-grounded before the spin coating is carried out. In order to optimize the test cells with graphene-added electrodes, preliminary studies were conducted to select suitable layers and find appropriate graphene content. Preliminary observations confirmed that the addition of 1% of graphene to slurry used for 4 th layer preparation gives solar cells performance enhancement. The improved (graphene added) 4 th layer was prepared following the spin coating and sintering process used for the preparation of the 4 th layer. To prepare the graphene added photoanode, 0.005 g of graphene was added to the TiO 2 slurry and well-grounded prior to spin coating. This slurry was used to coat the 4 th layer of the photoelectrode. The configuration of the photoanode prepared with 6 successive layers of spin-coated TiO 2 nanoparticle layers is illustrated schematically in Figure 01. 2.4 Preparation of the gel polymer electrolyte The optimized gel polymer electrolyte was prepared as per the stoichiometric composition of (EO) 10 (EC) 40 (PC) 40 LiI (1.2) (Hex 4 NI) (0.8) (4-TBP) (0.85) (MPII) 0.25 I 2(0.2) where the abbreviation EO represents one monomer unit of the polymer PEO [ 28 ]. As the initial step for the preparation of the electrolyte, appropriate amounts of Hex 4 NI, LiI, MPII, and 4-TBP were dissolved in PC and EC co-solvents mixture in a closed vial. Then, after adding the appropriate amount of PEO, the mixture was stirred continuously until a homogenous mixture was obtained. Afterward, the mixture was heated up to 100 °C with constant stirring until it was converted into a transparent slurry. Finally, the mixture was cooled down to 40 °C, and 1 2 (11.5 mg) was added, and the mixture was stirred well. The resulting gel polymer electrolyte from this process was characterized and utilized for solar cell fabrication. The relevant molar ratios and weights for the electrolyte are given in Table 01. Table 1: The weight composition and molar ratios of polymer (PEO), solvents (EC and PC), performance enhancers (MPII and 4-TBP), and iodide salts in the gel polymer electrolyte Component Weight/ mg Molar ratio PEO 100.0 10.0 PC 927.0 40.0 EC 800.0 40.0 MPII 15.1 0.25 Hex 4 NI 87.5 0.80 LiI 36.5 1.20 4-TBP 26.1 0.85 I 2 11.5 0.20 2.5 Fabrication of the DSSC Two different DSSCs were assembled by sandwiching the gel polymer electrolyte between a Pt-coated glass counter electrode and a dye-sensitized TiO 2 photoelectrode with 6 spin-coated TiO 2 layers. One DSSC contained the photoelectrode prepared by incorporating graphene into the 4 th layer. 3. Characterization 3.1 Characterization of the photoelectrode The X-ray diffraction (XRD) technique was utilized for crystallographic characterization of the photoanode. Cu K-α radiation wavelength 1.5405 Å from the Rigaku Ultima-IV X-Ray Diffractometer (KYOWAGLAS-XATM, Japan) was used to generate the XRD patterns of the TiO 2 film. In order to get the XRD spectrum, two single-layer electrodes were prepared with and without graphene in the same way the 4th layer was prepared. The scanning electron microscopic (SEM) images of the TiO 2 film were taken using Zeiss EVO-LS15 SEM. These images of the films were used to investigate the morphology of the TiO 2 films and the thickness of the photoanode. 3.2 Characterization of the DSSC Finally, the fabricated DSSCs were irradiated with PEC-LO1 solar simulator. By keeping the active area of the cell at 19 mm 2 and by varying the light intensity, current-voltage ( I-V) data were measured with a potential scan rate of 10 mV s − 1 using Keithley 2400 source meter and Pecell software. The light intensity was varied by changing the distance from the solar simulator to the cells. The obtained data were used to calculate the solar cell performance parameters J sc, V oc , ff , and the PCE of the cell. The PCE of the cell at variable intensity levels was calculated using; $$PCE= \frac{{P}_{max}}{I}$$ 1 where \({P}_{max}\) is the maximum power output of the cell and I is the irradiance of the incident light. The fill factor ( FF ) of the cell was determined using; $$FF= \frac{{P}_{max}}{{V}_{OC}{J}_{SC}}$$ 2 Therefore, $$PCE= \frac{FF {V}_{OC} {J}_{SC}}{{P}_{solar}}$$ 3 Equation ( 3 ) was used to calculate the intensity-dependent PCE values which are tabulated in Table 2 . 3.3 Electrochemical impedance spectroscopy Electrochemical impedance spectroscopy (EIS) data of the solar cells and electrolytes were measured by a Potentiostat (Autolab PGSTAT128N) together with a frequency response analyzer (FRA) module. Impedance data were collected with NOVA 1.1 software. During the measurements, the cells were placed in a Faraday cage. The EIS measurements of solar cells were done by applying a bias voltage similar to the V oc of the respective cells. To get EIS data of electrolytes, sample cells were prepared by sandwiching the electrolyte between two stainless steel electrodes. The measurement frequency window was 0.1 Hz − 1000 kHz and scanning was conducted with 80 steps. 4. Results and Discussion Understanding the variation in electrical conductivity of PEO-based electrolytes with temperature is crucial for optimizing electrolytes for different operating conditions. The ionic conductivities were calculated using the complex impedance data provided in Figure 2 (a). The Arrhenius equation aids in predicting conductivity trends and provides insights into the activation energy of charge carriers. The ionic conductivity obtained using complex impedance measurements is depicted in Figure 2 (b) as a function of 1000/ T , where T represents the electrolyte temperature. The top axis of the plot in Figure 2 (b) specifies the electrolyte temperature. The electrolyte exhibits an ionic conductivity of 3.37 mS cm -1 at 293.0 K, which increases to 7.31 mS cm -1 at 353.0 K. The data presented in Figure 2 (b) were fitted to the following equation: 4.2 XRD measurements The XRD pattern for the 4 th layer prepared with TiO 2 and graphene is given in Figure 03. The 2 θ values along with relevant TiO 2 phases and crystal planes are marked. Most of the peaks correspond to the dominant anatase phase of TiO 2 (101, 004, 200) and the presence of several characteristic peaks in the XRD spectra provides evidence for the polycrystalline nature of the TiO 2 films. Peaks (110) and (101) correspond to the rutile phase of TiO 2 and the origin of the peak (110) FTO is due to the diffraction pattern associated with FTO glass. In comparison, (101)A, (111)R, and (200)A peaks have become broader for graphene-free samples, which can be attributed to the smaller size of crystallites or an increase in lattice defects in graphene-free samples. Furthermore, the intensity of reflection from the (004)A plane has diminished in the graphene-free sample since it is not a preferred orientation of the sample. In Figure 03 (a), the peak related to graphene is clearly seen at (001) crystal plane. However, the intensity of the peak is not as strong as TiO 2 peaks because only 0.005 g (1% w/w) of graphene has been used to fabricate the photoanode. The absence of significant carbon peaks can be due to the dominance of TiO 2 content (99%) in the electrode. 4.3 Raman spectroscopy Figure 04 shows the Raman spectra of the exfoliated graphene. Two dominant peaks are visible namely the G band and 2D band at intensities 1580 cm -1 and 2730 cm -1 , respectively. The occurrence of the G band is due to the stretching vibrational motion of SP 2 hybridization of carbon-carbon bonds, and the peak position occurs at 2730 cm -1 is a characteristic signature of graphene [26]. The number of layers in exfoliated graphene was calculated using the intensity ratios between 2D and G peaks (I 2D /I G ). According to the experimental results, the value obtained for I 2D /I G ratio is 1.43. This data confirmed the successful synthesis of double layered graphene [26]. This exfoliated double layered graphene synthesized directly from vein graphite is used to fabricate the photoanodes of the solar cells investigated in this study. SEM images of the fabricated photoelectrodes at a magnification of 100,000 are shown in Figure 4. Figure 4(a) shows the top surface morphology of a 4-layer photoelectrode fabricated without graphene in the 4 th layer while Figure 4(b) shows the improved photoelectrode by adding graphene to the 4 th layer. When comparing the morphologies of these two layers, it can be observed that 4 layered electrodes prepared by adding graphene to the 4 th layer (Figure 4(b)) consist of graphene sheets. The presence of graphene in the 4 th layer can enhance the conductivity in the photoelectrode and alter the dye adsorption properties as well as influence the photocurrent, PCE, and fill factor of the DSSCs. Also, the presence of graphene may minimize the charge transfer resistances at the interfaces of the TiO 2 layer by faster electron transport which can hinder recombination. In addition, graphene can contribute to efficiency enhancement by improving light scattering as well. Figures 4(c) and 4(d) show the top surface morphology of the two 6-layer photoelectrodes prepared without and with graphene to the 4 th layer, respectively. These images confirm the formation of crack-free, nanocrystalline mesoporous thin films with high porosity that offer a large surface area for dye absorption. As we can see, these two images (Figure 4(c) and 4(d)) both look identical in the surface morphology because the same procedures and steps have been repeated to fabricate the 6 th layer electrodes except for the 4 th layer. The image in 4(d) confirms there are no graphene sheets visible. Therefore, the graphene in the 4 th layer is well covered by the 5 th and 6 th TiO 2 layers. 4.4 Dependence of Cell Performance on Irradiance Level Solar cell characteristics were evaluated as a function of intensity by taking I - V characteristic curves. Both graphene-added and graphene-free cells exhibited typical dye-sensitized solar cell behavior but with variations in their parameters. The plots for current density vs. cell potential ( J - V ) and power density vs. cell potential ( P - V ) are shown in Figure 06. The J - V and P - V curves of the graphene-added DSSCs at each intensity level are given in Figures 06(a), and 06(b), respectively. The J - V and P - V curves of the graphene-free control DSSCs at each intensity level are shown in Figures 05 (c) and(d), respectively. The photocurrent density and output power density of both cells decrease with decreasing intensity due to the reduction of photon flux and thus resulting in low photoelectron generation. The J - V and P - V characteristic curves in Figure 06 are used to determine the open-circuit voltage ( V oc ), the short circuit current density ( J sc ), the fill factor ( ff ), and the PCE of the fabricated DSSC under different irradiation levels. The values calculated for graphene-free DSSC (control cell) at different intensity levels are given in Table 03 while the respective values for the graphene-added cell (test cell) are given in Table 04. The cell fabricated without graphene in the 4 th layer exhibited significantly low performance compared to that of the graphene-added cell. The fabricated DSSC without graphene achieved 5.39% of efficiency under 1108 W m -2 irradiance while that in graphene added cell is 6.43%. With the gradual decrease of light irradiance level, the PCE of the cells increases though the net power output drops. This PCE increase observed in both cells with decreasing irradiance is attributed to an increase in fill factor which indicates the decrease in resistive losses (Tables 03 and 04). For example, the PCEs of graphene-free and graphene -added cells increase from 5.05% to 6.82% under one sun illumination (1000 W m -2 ). Consequently, the highest PCE and ff are exhibited at the lowest tested irradiance level of 67 W m -2 . The PCEs of graphene-free and graphene-added cells increase to 6.68% and 9.40% under 67 W m -2 intensity level. With the results obtained from both cells, it is evident that the efficiency and fill factor of the DSSCs increase with the decrease of irradiation. Achieving higher efficiencies in dye-sensitized solar cells under low light intensities agrees with the literature [ 29 , 30 , 31 ]. Further in both the cells ff has increased with decreasing light intensity. It can be due to reduced, recombination kinetics, non-radiative thermalization losses and charge transport losses. At the lower intensities, the generation of electron-hole pairs in the photoelectrode is less. This decreases the probability of carrier recombination before reaching the electrodes. Therefore, cells exhibit higher photocurrent at maximum power output contributing to a higher fill factor. At lower intensities, a smaller number of photons are available to excite electrons. Therefore, along with decreasing carrier generation and associated non-radiative recombination and thermalization of charge carriers decrease contributing to enhancing the fill factor. Since current and number charge carriers at lower light intensities are less, the resistive losses due to diffusion and the resistances are low and hence a higher fill factor can be expected. Table 2: Calculated values for the V OC , J SC , ff, ŋ, and the maximum power of the cell under different irradiation levels for cells prepared without adding graphene to the 4 th layer. Intensity / W m -2 V oc / V J sc / mA cm -2 V opt / V J opt / mA cm -2 P max / W ŋ /% ff /% 1108 0.7 12.3 0.53 11.3 5.98 5.39 69.6 1000 0.7 11.0 0.53 10.38 5.5 5.50 71.2 607 0.7 7.24 0.53 6.80 3.61 5.94 71.2 381 0.69 4.56 0.54 4.25 2.30 6.02 72.9 251 0.68 3.13 0.54 2.92 1.58 6.29 74.1 180 0.67 2.24 0.54 2.11 1.14 6.33 76.1 136 0.66 1.67 0.54 1.60 0.86 6.35 78.2 104 0.65 1.32 0.54 1.25 0.67 6.48 78.7 85 0.64 1.08 0.54 1.04 0.56 6.59 80.9 67 0.63 0.87 0.55 0.81 0.45 6.68 81.5 Table 3: Calculated values for the V OC , J SC , ff, ŋ, and the maximum power of the cell under different irradiation levels for cells prepared by adding graphene into the 4th layer. Intensity / W m -2 V oc / V J sc / mA cm -2 V opt / V J opt / mA cm -2 P max / W ŋ /% ff /% 1108 0.74 17.0 0.47 15.2 7.12 6.43 56.5 1000 0.77 13.4 0.54 12.6 6.82 6.82 66.2 607 0.71 9.69 0.50 8.97 4.49 7.40 65.2 381 0.71 6.34 0.52 5.92 3.08 8.07 68.3 251 0.70 4.20 0.53 3.98 2.11 8.41 71.9 180 0.69 3.02 0.54 2.88 1.55 8.62 74.5 136 0.69 2.27 0.55 2.17 1.20 8.79 76.3 104 0.68 1.73 0.55 1.70 0.94 9.01 79.5 85 0.68 1.42 0.55 1.42 0.78 9.23 81.3 67 0.68 1.11 0.55 1.15 0.63 9.40 83.1 4.5 Incident photon-to-current efficiency (IPCE) IPCE measurements offer valuable insight into the spectral response and performance of a DSC across the solar spectrum. By varying the wavelength of the incident light, the obtained IPCE spectrums for the two distinct variants of the fabricated solar cells are given in Figure 7. The reference solar cell is composed of a photoanode solely made of TiO 2 nanoparticles which provides a baseline for comparison. During characterization, it exhibits moderate IPCE values with a single narrow absorption peak. This graphene-free cell exhibits a maximum IPCE of 40.65 at 525 nm. The test cell, enhanced with graphene, shows higher IPCE with two distinctive peaks at ~345 nm and ~530 nm along with IPCE of 44.35 and 53.76%. The IPCE value is usually determined by the charge collection at the collecting electrode and dye loading capacity. With added graphene on TiO 2 could capture and shuttle electrons quickly to the collecting electrodes which leads to the improvement of the IPCE value of the graphene-based solar cell over the entire wavelength of the spectrum [ 32 , 33 ]. 4.6 Electrochemical impedance (EIS) spectroscopy In order to get further insight into the higher efficiency of the test cell, EIS data is utilized. Figures 8 (a) and 8 (b) represent the Nyquist plots and Bode phase diagrams for the two cells. Using the impedance spectra Bode diagram was plotted and estimated the values of electron transport lifetime ( t tr ), recombination lifetime ( t rec ) and diffusion length ( D L ) are given in Table 5. The D L is the average distance traveled by a charge carrier within the semiconducting material before it recombines. This length plays a crucial role in determining the efficiency of charge carrier transport and lifetime inside the cell. In this study, D L was calculated by following the equation, along with the impedance data analysis [ 34 , 35 , 36 ]. Where, R tr and R rec represent the charge transfer resistance and recombination resistance. L is the layer thickness [ 37 ]. Nyquist plots in Figure 8 (a) were used to determine the R tr and R rec for each cell and layer thickness was measured using high-resolution scanning electron microscopy ( L = 5.2 mm). Table 4: Recombination lifetimes (t rec ), electron transport lifetimes (t tr ) and diffusion lengths (D L ) of the prepared DSCs. Cell ( L )/ m m t rec / mS t tr / mS D L / m m DSC with TiO 2 /Graphene photoelectrode 5.2 3.22 0.34 7.1 DSC with TiO 2 only photoelectrode 5.2 2.43 0.25 6.2 Interestingly the study shows the DSC fabricated with TiO 2 and graphene has a higher diffusion length value than that of the reference cell. The increased diffusion length enhances the likelihood that the charge carriers will reach the electrodes contributing to enhancing collection efficiency. In a DSC photogenerated electrons and holes are separated at the dye-semiconductor interface. However, a certain number of charge carriers recombine instead of traveling through the external circuit, which could negatively impact the overall performance of the solar cell. By increasing the recombination lifetimes, it is possible to prolong the duration of which these electron-hole pairs remain separated. This prolonged duration allows more charge carriers to reach the electrodes and contribute to the photo-current. The study shows the fabricated solar cell with TiO 2 and graphene contains higher recombination lifetimes compared to the reference cell. This longer lifetime may have impacted positively to improve cell efficiency. 4.7 Effect of graphene on cell performance The cell fabricated by adding graphene shows higher V OC , J SC , ff , and PCE compared to the cell without graphene. The observed performance enhancement is very likely due to the positive effects imposed by the incorporated graphene. For a better visualization of the behavior PCE and ff variations of the cells with light intensity are shown in Figure 9 (a) and (b) respectively. Graphene has excellent electrical conductivity and optical properties, enabling it to enhance the absorption of light and facilitate efficient charge transport within the solar cell, leading to higher conversion efficiencies and increased power output. The improved performance with added graphene observed in this study can be attributed to the combined effects of the following process. Decreased charge transport resistance of the photoelectrode and charge transfer resistance between two interfaces of TiO 2 as a result of increased conductivity [ 38 , 39 ]. The reduction of resistive losses improves the photocurrent of the cell. The decrease of resistive losses with added graphene is inferred by the higher ff shown by the graphene-incorporated cell. The improved charge transfer between the FTO current collectors indirectly helps to reduce the recombination losses. The behavior is evident by the increase of V OC , and ff of the graphene-added cell. This process enables more efficient conversion of light energy to electricity. The V oc enhancement can be contributed by faster electron extraction by graphene added interlayer from the excited dye molecules [ 40 , 41 ]. Graphene's large surface area and high carrier mobility facilitate improved electron injection from the excited dye molecules to the Graphene/TiO 2 layer, thereby enhancing the efficiency of the dye to photoelectron conversion process. This can also reduce energy loss due to non-radiative decay. Graphene's large surface area can facilitate the distribution of TiO 2 and thus can enhance the effective surface area available for dye adsorption by the electrode as inferred by analyzing SEM images. This promotes higher dye loading, leading to increased light absorption and improved device performance. Finally, it can be deduced that the DSSC made with graphene-added photoelectrode- exhibited impressive efficiency enhancement under low irradiation. For instance, the addition of 1% of graphene to the 4 th TiO 2 layer of the photoanode improves the efficiency of the cell from 5.50% to 6.82% under one sun illumination (1000 W m -2 ). This is a 24% efficiency improvement. Efficiency enhancements given by the graphene-added DSSC with respect to graphene-free solar cells (control device) are given in Table 6 for different irradiance levels. Table 5: Efficiency enhancements by the graphene-incorporated photo electrode-based DSSCs with respect to the graphene-free solar cell. Intensity / W m -2 1108 1000 607 381 251 180 136 104 85 67 Efficiency enhancement /% 19.3 24 24.6 34.1 33.7 36.2 38.4 39.0 40.1 40.7 The present study shows that not only graphene can be used to enhance DSSC performance but also that graphene can be successfully synthesized from natural vein graphite using a scalable and cost-effective method. 4. Conclusions This study reports efficiency enhancements in graphene-incorporated, quasi-solid-state DSSCs under ambient and low-light conditions. The XRD results and high-resolution SEM images confirmed the presence of anatase TiO 2 nanoparticles in photoelectrodes. The Raman spectroscopy confirmed the successful fabrication of two-layer graphene from the vein graphite. One of the challenges of widely utilizing graphene in solar cells is their high cost. This study presents a cost-effective, feasible, and novel method to exfoliate vein graphite sourced directly from the mine site and a strategic way to integrate them in photoanodes. SEM images confirm the presence of graphene in the most effective layer of the photoanode. The PCEs of 5.05% graphene-free cells (control cell) increased to 6.82% with the integration of graphene into the photoanode, exhibiting 24% enhancement at ambient irradiation. The V oc , J sc , and ff , values of graphene-incorporated DSSC are 6.82%, 770 mV, 13.4 mA cm − 2 , and 66.2% respectively at 1000 W m − 2 . Notably, the efficiency and fill factor exhibited an intriguing increase at lower light intensities. The synthesized graphene incorporated DSSC achieved a remarkable efficiency of 9.4% and a fill factor of 83.1% at 67 W m − 2 solar irradiance. The efficiency enhancement for 67 W m − 2 intensity compared to 1000 W m − 2 is ∼38%. The performance of the improved DSSC by integrating the synthesized graphene from vein graphite outperforms the reference cell at all the intensities measured. This improved efficiency is attributed to the higher charge carrier recombination lifetime (3.22 mS) and high diffusion lengths (7.1 µm) of the improved DSC by integrating graphene into to photoanode. Declarations Funding The authors would like to acknowledge the financial support from the Postgraduate Institute of Science, University of Peradeniya (grant No. PGIS/2020/10), and Peradeniya University Research Grant No. 2023/34/S. Author Contribution T.M.W.J. Conceptualization, Methodology, Project administration and Supervision, Writing, Reviewing Editing fund acquisition and Formal analysis.S.M.S.G. Data collection, Formal analysis and measurement, 1st draft preparation. G.G.D.M.G.G: Data collection, Formal analysis and measurement.B.M.K.P., Writing, Reviewing, Editing and Formal analysis. L.A.DeS.,Writing, Reviewing, Editing and Formal analysis. M.A.K.L.D. and G.R.A.K., Writing, Reviewing, Editing and Formal analysis. Acknowledgement The authors would like to acknowledge Udara Wadasinghe in University Peradeniya, for the technical support given for this project. 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Bandara, TMWJ., SMSGunathilake, GBMMMNishshanke, MAKLDissanayake, NBChaure, OIOlusola, B-EMellander, MFurlani, and Ingvar Albinsson"Efficiency enhancement and chrono-photoelectron generation in dye-sensitized solar cells based on spin-coated TiO2 nanoparticle multilayer photoanodes and a ternary iodide gel polymer electrolyte." Journal of Materials Science: Materials in Electronics 34, no28 (2023): 1969. Wang, YC., & Cho, CP(2017)Application of TiO2-graphene nanocomposites to photoanode of dye-sensitized solar cellJournal of Photochemistry and Photobiology A: Chemistry, 332, 1-9. Tao, E., Ma, Z., Yang, S., Li, Y., Ma, D., Xing, Z., & Li, Y(2020)Enhanced electrical conductivity of TiO2/graphene: The role of introducing Ca2+Journal of Alloys and Compounds, 827, 154280. Das, S., Sudhagar, P., Kang, YS., & Choi, W(2014)Graphene synthesis and application for solar cellsJournal of Materials Research, 29(3), 299-319. Su, H., & Hu, YH(2023)3D graphene: synthesis, properties, and solar cell applicationsChemical CommunicationsDOI https://doi.org/10.1039/D3CC01004J Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 23 Sep, 2024 Read the published version in Journal of Applied Electrochemistry → Version 1 posted Editorial decision: Revision requested 18 Aug, 2024 Reviews received at journal 17 Aug, 2024 Reviewers agreed at journal 01 Aug, 2024 Reviews received at journal 10 Jul, 2024 Reviewers agreed at journal 23 Jun, 2024 Reviewers agreed at journal 21 Jun, 2024 Reviewers invited by journal 13 May, 2024 Editor assigned by journal 02 May, 2024 Submission checks completed at journal 29 Apr, 2024 First submitted to journal 27 Apr, 2024 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-4335227","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":297898531,"identity":"684c6965-efa4-4e22-b8cc-b50744bdfb43","order_by":0,"name":"T. M. W. J. Bandara","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0UlEQVRIiWNgGAWjYFACxgYDBgZmBn4GBjYStUg2EK8FDJgZDA4Qq4V/RnJDwccd1vnGN5KfPfhQwSDPL3YAvxaJG4kNhjPPpFtuu5FmbjjjDIPhzNkJBKy5ndhgzNt22MDsRoKZNG8bQ4LBbQJa5EFa/gK1GM9I/0acFgOQFkagFgOJHCJtMbz/sMGwty3dQOLMmzLJGWckCPtF7szxZwY/26wN+NvTt0l8qLCR55cmoAUI2AzAlABYpQRB5SDA/ABM8R8gSvUoGAWjYBSMQAAAzLxDZ4QYrMAAAAAASUVORK5CYII=","orcid":"","institution":"University of Peradeniya","correspondingAuthor":true,"prefix":"","firstName":"T.","middleName":"M. W. J.","lastName":"Bandara","suffix":""},{"id":297898533,"identity":"effa38b9-79fb-484f-8512-ce358a2f8ec8","order_by":1,"name":"S. M. S. Gunathilake","email":"","orcid":"","institution":"University of Peradeniya","correspondingAuthor":false,"prefix":"","firstName":"S.","middleName":"M. S.","lastName":"Gunathilake","suffix":""},{"id":297898535,"identity":"01e7477e-e139-4e41-beb1-6f1e74861ae6","order_by":2,"name":"G. G. D. M. G. Gamachchi","email":"","orcid":"","institution":"University of Peradeniya","correspondingAuthor":false,"prefix":"","firstName":"G.","middleName":"G. D. M. G.","lastName":"Gamachchi","suffix":""},{"id":297898538,"identity":"0f759de6-f021-42f3-8a24-fb4acb58276c","order_by":3,"name":"B. M. K Pemasiri","email":"","orcid":"","institution":"University of Peradeniya","correspondingAuthor":false,"prefix":"","firstName":"B.","middleName":"M. K","lastName":"Pemasiri","suffix":""},{"id":297898541,"identity":"01922b16-984f-4be9-b5e9-a21d6d0a2783","order_by":4,"name":"L. Ajith DeSilva","email":"","orcid":"","institution":"University of West Georgia","correspondingAuthor":false,"prefix":"","firstName":"L.","middleName":"Ajith","lastName":"DeSilva","suffix":""},{"id":297898543,"identity":"386234ad-f1ee-45c2-a9c8-ae2cc5be7e69","order_by":5,"name":"M. A. K. L. Dissanayake","email":"","orcid":"","institution":"National Institute of Fundamental Studies","correspondingAuthor":false,"prefix":"","firstName":"M.","middleName":"A. K. L.","lastName":"Dissanayake","suffix":""},{"id":297898545,"identity":"3e6d8dc5-1ea2-464c-80b4-db3f13905048","order_by":6,"name":"G. R. A. Kumara","email":"","orcid":"","institution":"University of West Georgia","correspondingAuthor":false,"prefix":"","firstName":"G.","middleName":"R. A.","lastName":"Kumara","suffix":""}],"badges":[],"createdAt":"2024-04-27 18:56:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4335227/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4335227/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10800-024-02204-x","type":"published","date":"2024-09-23T15:57:19+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":56039569,"identity":"9157a08a-7bba-4965-bc7a-b6dcd9231596","added_by":"auto","created_at":"2024-05-07 19:12:39","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":25302,"visible":true,"origin":"","legend":"\u003cp\u003eA schematic diagram to illustrate the configuration of the multilayer photoelectrodes investigated in this study: (a) without graphene and (b) with graphene in the 4\u003csup\u003eth\u003c/sup\u003e layer\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/915b57863ff58ffa62612e29.png"},{"id":56039573,"identity":"ce00fc5a-c09d-4ea2-a6a7-dd47eda5ad48","added_by":"auto","created_at":"2024-05-07 19:12:40","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":53219,"visible":true,"origin":"","legend":"\u003cp\u003ea) Complex impedance plots of the electrolyte at different temperatures, b) the graph of conductivity (\u003cem\u003eσ\u003c/em\u003e) versus 1000/\u003cem\u003eT\u003c/em\u003e obtained using complex impedance measurements\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/ea39c47bd7b1b04cafd984a7.png"},{"id":56039567,"identity":"505e0b4b-16d9-4577-b528-bb7e12ff3296","added_by":"auto","created_at":"2024-05-07 19:12:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":83508,"visible":true,"origin":"","legend":"\u003cp\u003eXRD spectra of the 4\u003csup\u003eth\u003c/sup\u003e layer prepared with (a)TiO\u003csub\u003e2\u003c/sub\u003e and 1% graphene, (b) TiO\u003csub\u003e2\u003c/sub\u003e only\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/8f91510bf150d6b3f575de6a.png"},{"id":56040915,"identity":"942d6f84-ab64-42d1-9e07-faed4ce683a3","added_by":"auto","created_at":"2024-05-07 19:20:40","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":37410,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectra of the exfoliated graphene samples.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/df9bce6b0bcbb412c242c3e2.png"},{"id":56040913,"identity":"1fb2e9c2-7aa1-4718-856f-ca12f71d2257","added_by":"auto","created_at":"2024-05-07 19:20:39","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":292026,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The SEM image of the 4\u003csup\u003eth\u003c/sup\u003e layer of the TiO\u003csub\u003e2\u003c/sub\u003e electrode prepared without adding graphene, (b) SEM image of the 4\u003csup\u003eth\u003c/sup\u003e layer of the electrode prepared by adding graphene to the 4\u003csup\u003eth\u003c/sup\u003e layer. SEM images of the 6-layer photoanodes prepared (c) without adding graphene and (d) SEM image of the top (6\u003csup\u003eth\u003c/sup\u003e) layer of the electrode prepared by adding graphene to the 6\u003csup\u003eth\u003c/sup\u003e layer.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/961b0fac8ea5c487987c9f25.png"},{"id":56039570,"identity":"05110e34-879b-423a-a6e9-e757f259ae81","added_by":"auto","created_at":"2024-05-07 19:12:40","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":135420,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Current density vs. cell potential curves for the cell prepared without graphene (b) Current density vs. cell potential curves for the cell prepared by adding graphene to the 4th layer (c) Power density vs. cell potential curves for the cell prepared without graphene (d) power density vs. cell potential curves for the cell prepared by adding graphene to the 4\u003csup\u003eth\u003c/sup\u003e layer.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/f08d1d2f5a8bdcac81223dfa.png"},{"id":56039572,"identity":"3341be39-e70d-43ad-9dc8-8fe0b5fee043","added_by":"auto","created_at":"2024-05-07 19:12:40","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":437962,"visible":true,"origin":"","legend":"\u003cp\u003eIPCE spectra of the DSCs with TiO\u003csub\u003e2\u003c/sub\u003e photoelectrode and graphene TiO\u003csub\u003e2 \u003c/sub\u003eadded\u003csub\u003e \u003c/sub\u003ephotoelectrode.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/4a32ae519d1cdef978486936.png"},{"id":56039575,"identity":"2b9f1c2d-7632-4316-97f5-ec5ec2d520e3","added_by":"auto","created_at":"2024-05-07 19:12:40","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":46564,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The Nyquist plots and (b) the Bode phase diagrams for the two prepared DSCs.\u003c/p\u003e\n\u003cp\u003eThe \u003cem\u003eD\u003c/em\u003e\u003csub\u003eL\u003c/sub\u003e is the average distance traveled by a charge carrier within the semiconducting material before it recombines. This length plays a crucial role in determining the efficiency of charge carrier transport and lifetime inside the cell. In this study, \u003cem\u003eD\u003c/em\u003e\u003csub\u003eL\u003c/sub\u003e was calculated by following the equation, along with the impedance data analysis [\u003csup\u003e34\u003c/sup\u003e, \u003csup\u003e35\u003c/sup\u003e, \u003csup\u003e36\u003c/sup\u003e].\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/09c48ae394014d596c725fe4.png"},{"id":56040914,"identity":"c909a796-0e7a-4879-bd20-33932624071b","added_by":"auto","created_at":"2024-05-07 19:20:40","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":56666,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Efficiency variation of the cells with light intensity, and (b) Variation of the fill factor of the cells with light intensity.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/8506eecf9376dbdbd1422914.png"},{"id":65627165,"identity":"542a1f60-1655-4884-aebc-81ad8d59c6ac","added_by":"auto","created_at":"2024-09-30 16:12:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1814456,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4335227/v1/4c0382a1-c905-44e7-a3ce-57f413e4a631.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Strategic Integration of Graphene into Multilayer Photoanode; Enhancing Efficiency of Quasi-Solid-State Dye-Sensitized Solar Cells Under Ambient and Low Irradiance","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOne of the biggest challenges in the 21\u003csup\u003est\u003c/sup\u003e century is to replace fossil fuels with renewable and more environmentally friendly energy sources while supplying the ever-increasing energy demand. The development of low-cost and efficient solar cells with emerging technologies is the long-term solution to this energy crisis [\u003csup\u003e1\u003c/sup\u003e,\u003csup\u003e2\u003c/sup\u003e,\u003csup\u003e3\u003c/sup\u003e]. Due to the lower production costs and the relatively high-power conversion efficiency (PCE), dye-sensitized solar cells (DSSCs) have received greater attention from researchers during the last decade [\u003csup\u003e4\u003c/sup\u003e,\u003csup\u003e5\u003c/sup\u003e,\u003csup\u003e6\u003c/sup\u003e].\u0026nbsp;DSSCs have attained a maximum power conversion efficiency of 15.0% liquid electrolytes under ambient conditions [\u003csup\u003e7\u003c/sup\u003e].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe photoanode in a DSSC plays a key role in absorbing light energy and producing current and voltage through photoexcitation. The photoanode consists of a transparent conductive oxide (TCO) layer coated on a glass substrate. On top of this layer lies the mesoporous nanocrystalline wide-bandgap semiconducting material (TiO\u003csub\u003e2\u003c/sub\u003e). The power conversion efficiency of a DSSC is basically governed by the properties of the photoanode. A high-performing photoanode should have a large specific surface area for more dye adsorption, faster electron transport, high resistance to photo-corrosion, high electrical conductivity, and excellent interfacial contact between the dye molecules and the electrolyte [\u003csup\u003e8\u003c/sup\u003e, \u003csup\u003e9\u003c/sup\u003e]. By integrating highly conductive carbon nanostructures such as graphene, graphene oxide, carbon nanotubes and fullerene into TiO\u003csub\u003e2\u003c/sub\u003e photoelectrode, DSSC performance can be enhanced due to the improved charge transport properties TiO\u003csub\u003e2\u003c/sub\u003e composite electrode. Among these carbon materials, graphene stands out due to its remarkable properties such as excellent optical transmittance, tunable bandgap, high specific surface area, and high mechanical strength. Further, with the addition of graphene or graphene quantum dots, the PCE of DSSCs can be improved through up-conversion and down-conversion [\u003csup\u003e10\u003c/sup\u003e,\u003csup\u003e11\u003c/sup\u003e,\u003csup\u003e12\u003c/sup\u003e], broadening the spectral absorption of the photoelectrode [\u003csup\u003e13\u003c/sup\u003e] and improving electron mobility.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFang et al. first [\u003csup\u003e14\u003c/sup\u003e] reported graphene quantum dot (GQD) assisted dye sensitized TiO\u003csub\u003e2\u003c/sub\u003e photoelectrodes demonstrating an efficiency of 6.10%, making 19.6% enhancement with GQD inclusion. Fan et al. [\u003csup\u003e15\u003c/sup\u003e] reported a TiO\u003csub\u003e2\u003c/sub\u003e/graphene nanocomposite-based DSSC with 5.77% efficiency which is a 25% enhancement over graphene-free cell. This efficiency improvement is attributed to reduced electrode-electrolyte interfacial resistance, diminished charge recombination rates, enhanced light scattering, and the enhancement of charge transport resulting from the addition of graphene. Pattarith. K et al. [\u003csup\u003e16\u003c/sup\u003e], report higher efficiency of 9.15% for the cell optimized using graphene, benefiting from enhanced dye loading, improved of electronic conductivity, and reduced recombination. For an optimized TiO\u003csub\u003e2\u003c/sub\u003e photoelectrodes with RGO and graphene, Tang. B et al. [\u003csup\u003e17\u003c/sup\u003e] achieved a state-of-the-art efficiency of 11.8% for optimized TiO\u003csub\u003e2\u003c/sub\u003e photoelectrodes with reduced graphene oxide (RGO) and graphene. The reported higher efficiency is related to enhanced light scattering and the increased surface area for dye adsorption. The above efficiencies have been reported using problematic liquid electrolytes and ambient 1000 W m\u003csup\u003e-2\u003c/sup\u003e irradiance.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe performance of a DSSC or any other solar cell mainly depends on the intensity of photon flux /solar irradiation incident to the cell. In nature, sunlight intensity does not remain constant throughout the day or year. Some studies have shown that the efficiency of traditional Si-based solar cells decreases with the decreasing irradiance level [\u003csup\u003e18\u003c/sup\u003e, \u003csup\u003e19\u003c/sup\u003e]. Only a few studies have been focused on investigating the performance of quasi-solid state DSSCs as a function of light intensity [\u003csup\u003e20\u003c/sup\u003e]. In addition, to our knowledge, there are no reported studies focused on investigating the performance of graphene-incorporated photoanode-based quasi-solid state DSSC. Therefore, it is very important to investigate DSSC performance variation with the light intensity in order to estimate the power generation at different times of the day.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn addition to graphene and graphene oxide various other carbon-based materials have also been explored for the improving photoanodes in DSSCs. However, each presents its unique set of advantages and disadvantages. Carbon nanotubes (CNTs) for instance, have gained attention due to exceptional electrical conductivity, high surface area, and tubular structure [\u003csup\u003e21\u003c/sup\u003e,\u003csup\u003e22\u003c/sup\u003e]. However, challenges such as CNT aggregation and difficulty of achieving uniform distribution on photoanode may have impacted their effective utilization in DSSCs. Carbon nanofibers (SNFs) are one-dimensional nanostructures similar to CNTs with good electrical conductivity and mechanical strength [\u003csup\u003e23\u003c/sup\u003e]. Despite their advantages, challenges in synthesizing and difficulty in proper alignment within the photoanode are considerable drawbacks. Carbon aerogels, a three-dimensional porous carbon structure offers a large surface area for dye adsorption and electron transport [\u003csup\u003e24\u003c/sup\u003e].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAccording to the literature, while relatively higher efficiencies are recorded for graphene added DSSCs compared to control devices, the highest efficiency achieved (15%) by conventional DSSCs has not yet been surpassed. Additionally, the complexity of synthesis and poor stability and scalability issues hindered their application. This field necessitates further research to develop effective strategies for integrating carbon-based materials such as graphene into DSSC photoanodes to address these challenges.\u003c/p\u003e\n\u003cp\u003eBy taking above mentioned key factors into account, the present study focuses on systematically incorporating a small amount of graphene into the multi-layer photoanode. Interestingly, in this study the integration of graphene into the 4\u003csup\u003eth\u003c/sup\u003e layer of the 6-layer TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003ephotoanode resulted in enhanced solar cell performance. In addition, one of the challenges of utilizing graphene in solar cells is their high cost. This study presents a low-cost feasible, and novel method for synthesizing graphene using vein graphite received directly from the mine site for incorporation into photoanodes. Another significance of this study is achieving higher efficiency for quasi-soid state configuration without relying on volatile solvent-based electrolytes in the DSSCs.\u0026nbsp;\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cp\u003e\u003cem\u003e2.1\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Materials\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTransparent and conducting FTO substrates having a sheet resistance of 10 \u0026Omega; cm\u003csup\u003e-2\u003c/sup\u003e and ruthenium-based 535-bisTBA (N719) dye sensitizer were purchased from Solaronix SA. Titanium dioxide nanopowders of average particle sizes of 21 nm (P25) and 13 nm (P21) were procured from Evonik, Germany. The starting materials for the preparation of the gel polymer electrolyte; iodine (I\u003csub\u003e2\u003c/sub\u003e), ethylene carbonate (EC), propylene carbonate (PC), 1-Methyl-3-propylimidazolium iodide (MPII) and 4-tert-butylpyridine (4-TBP) with purity greater than 98%, Tetrahexyl ammonium iodide, lithium iodide and Polyethylene oxide (MW = 4,000,000) were purchased from Sigma Aldrich. Before using, tetrahexyl ammonium iodide, lithium iodide and polyethylene oxide (PEO) were vacuum dried for about 2 h at 50 ℃.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.2\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Preparation\u003c/em\u003e of\u003cem\u003e\u0026nbsp;graphene\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eGraphene can be synthesized using various methods for applications [\u003csup\u003e25\u003c/sup\u003e]. In this study, the electrolyte solution for the exfoliation was prepared by dissolving 26.14 g of K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e in 300 mL of deionized water (0.5 M). Shiny slippery fibrous (SSF) natural Sri Lankan vein graphite obtained from the Kahatagaha mine site mining site was used as starting material [\u003csup\u003e26\u003c/sup\u003e]. \u0026nbsp; Two pieces of vein graphite samples were directly used as the anode and cathode. The separation between the two electrodes was kept at about 3 cm and electrochemical exfoliation of graphite was conducted by applying a 10 V (DC) between the two graphite electrodes for 2 hours. After that, the layer floating on the top of the exfoliated graphite (EG) suspension was collected and filtered using a PTFE membrane filter (0.2 \u0026micro;m pore size). Then, the EG was washed several times with DI water to remove residual salt and it was placed in the oven at 80 \u0026deg;C for 3 h.\u003c/p\u003e\n\u003cp\u003eFor further exfoliation, 1 g of electrochemically EG was added to 100 ml of DMF and it was sonicated for 3 hours in order to synthesize graphene as already reported [\u003csup\u003e27\u003c/sup\u003e]. After the sonication, the solution was stirred with the help of a magnetic stirrer for 24 hours in order to further minimize the particle size. The resulting solution was then oven-dried and the precipitate was used for the characterization and solar cell fabrication.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.3\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Preparation\u003c/em\u003e \u003cem\u003eof graphene added multilayer photoelectrode\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFor the preparation of 1\u003csup\u003est\u003c/sup\u003e and 2\u003csup\u003end\u003c/sup\u003e layers of TiO\u003csub\u003e2\u003c/sub\u003e photoanode, 0.5 g of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles with an average particle size of 13 nm (P90 powder) was mixed with 0.1 mol dm\u003csup\u003e-3\u003c/sup\u003e HNO\u003csub\u003e3\u003c/sub\u003e for about 30 minutes in an agate mortar with a pestle. In order to prevent the coating of TiO\u003csub\u003e2\u003c/sub\u003e in the area needed for FTO contacts, half of the FTO electrode was masked with scotch tape. Then, the TiO\u003csub\u003e2\u003c/sub\u003e slurry was spin-coated on a well-cleaned FTO substrate of 1 cm\u0026nbsp;\u0026acute;\u0026nbsp;2 cm size at 2300 rpm for 2 minutes. For this purpose, freshly prepared TiO\u003csub\u003e2\u003c/sub\u003e slurry was spread homogeneously on the FTO substrate with the help of a pestle, and spinning commenced immediately after the application of the TiO\u003csub\u003e2\u003c/sub\u003e slurry on the glass substrate, without allowing time for it to dry. \u0026nbsp;Subsequently, the photoelectrode was air dried at ambient conditions for 24 h and then, sintered in air at about 450 ℃ for 30 minutes. For the preparation of the 3\u003csup\u003erd\u003c/sup\u003e layer of the photoelectrode, 0.5 g of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles of particle size 21 nm (P25) was ground with 0.1 mol dm\u003csup\u003e-3\u003c/sup\u003e and the resulting slurry was spin-coated at 1000 rpm for 2 minutes and followed by sintering at 450 ℃.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe 4\u003csup\u003eth\u003c/sup\u003e, 5\u003csup\u003eth\u003c/sup\u003e and 6\u003csup\u003eth\u003c/sup\u003e TiO\u003csub\u003e2\u003c/sub\u003e layers were prepared following the spin coating and sintering process used for the 3\u003csup\u003erd\u003c/sup\u003e layer preparation, except that, 0.1 g of PEO (4,000,000 molar weight) and a few drops of Titron X 100 (surfactant) were added to the TiO\u003csub\u003e2\u003c/sub\u003e slurry and well-grounded before the spin coating is carried out. In order to optimize the test cells with graphene-added electrodes, preliminary studies were conducted to select suitable layers and find appropriate graphene content. Preliminary observations confirmed that the addition of 1% of graphene to slurry used for 4\u003csup\u003eth\u003c/sup\u003e layer preparation gives solar cells performance enhancement.\u003c/p\u003e\n\u003cp\u003eThe improved (graphene added) 4\u003csup\u003eth\u003c/sup\u003e layer was prepared following the spin coating and sintering process used for the preparation of the 4\u003csup\u003eth\u003c/sup\u003e layer. \u0026nbsp;To prepare the graphene added photoanode, 0.005 g of graphene was added to the TiO\u003csub\u003e2\u003c/sub\u003e slurry and well-grounded prior to spin coating. This slurry was used to coat the 4\u003csup\u003eth\u003c/sup\u003e layer of the photoelectrode. The configuration of the photoanode prepared with 6 successive layers of spin-coated TiO\u003csub\u003e2\u003c/sub\u003e nanoparticle layers is illustrated schematically in Figure 01.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.4\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Preparation of the gel polymer electrolyte\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe optimized gel polymer electrolyte was prepared as per the stoichiometric composition of\u0026nbsp;(EO)\u003csub\u003e10\u003c/sub\u003e(EC)\u003csub\u003e40\u003c/sub\u003e(PC)\u003csub\u003e40\u003c/sub\u003eLiI\u003csub\u003e(1.2)\u003c/sub\u003e(Hex\u003csub\u003e4\u003c/sub\u003eNI)\u003csub\u003e(0.8)\u003c/sub\u003e(4-TBP)\u003csub\u003e(0.85)\u003c/sub\u003e(MPII)\u003csub\u003e0.25\u003c/sub\u003eI\u003csub\u003e2(0.2)\u0026nbsp;\u003c/sub\u003ewhere the abbreviation EO represents one monomer unit of the polymer PEO [\u003csup\u003e28\u003c/sup\u003e].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAs the\u0026nbsp;initial\u0026nbsp;step for the preparation of the electrolyte, appropriate amounts of Hex\u003csub\u003e4\u003c/sub\u003eNI, LiI, MPII, and 4-TBP were dissolved in PC and EC co-solvents mixture in a closed vial. Then, after adding the appropriate amount of PEO, the mixture was stirred continuously until a homogenous mixture was obtained. Afterward, the mixture was heated up to 100 \u0026deg;C with constant stirring until it was converted into a transparent slurry. Finally, the mixture was cooled down to 40 \u0026deg;C, and 1\u003csub\u003e2\u003c/sub\u003e (11.5\u0026nbsp;mg) was added, and the mixture was stirred well. The resulting gel polymer electrolyte from this process was characterized and utilized for solar cell fabrication. The relevant molar ratios and weights for the electrolyte are given in Table 01.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;1: The weight composition and molar ratios of polymer (PEO), solvents (EC and PC), performance enhancers (MPII and 4-TBP), and iodide salts in the gel polymer electrolyte\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"519\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eComponent\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eWeight/ mg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eMolar ratio\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePEO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e100.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e927.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e40.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eEC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e800.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e40.0\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eMPII\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e15.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.25\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHex\u003csub\u003e4\u003c/sub\u003eNI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e87.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.80\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLiI\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e36.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.20 \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e4-TBP\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e26.1\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.85 \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eI\u003csub\u003e2\u003c/sub\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e11.5\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.20\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003e2.5 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Fabrication of the DSSC\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTwo different DSSCs were assembled by sandwiching the gel polymer electrolyte between a Pt-coated glass counter electrode and a dye-sensitized TiO\u003csub\u003e2\u003c/sub\u003e photoelectrode with 6 spin-coated TiO\u003csub\u003e2\u003c/sub\u003e layers. One DSSC contained the photoelectrode prepared by incorporating graphene into the 4\u003csup\u003eth\u003c/sup\u003e layer.\u003c/p\u003e"},{"header":"3. Characterization","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Characterization of the photoelectrode\u003c/h2\u003e \u003cp\u003eThe X-ray diffraction (XRD) technique was utilized for crystallographic characterization of the photoanode. Cu K-α radiation wavelength 1.5405 \u0026Aring; from the Rigaku Ultima-IV X-Ray Diffractometer (KYOWAGLAS-XATM, Japan) was used to generate the XRD patterns of the TiO\u003csub\u003e2\u003c/sub\u003e film. In order to get the XRD spectrum, two single-layer electrodes were prepared with and without graphene in the same way the 4th layer was prepared.\u003c/p\u003e \u003cp\u003eThe scanning electron microscopic (SEM) images of the TiO\u003csub\u003e2\u003c/sub\u003e film were taken using Zeiss EVO-LS15 SEM. These images of the films were used to investigate the morphology of the TiO\u003csub\u003e2\u003c/sub\u003e films and the thickness of the photoanode.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Characterization of the DSSC\u003c/h2\u003e \u003cp\u003eFinally, the fabricated DSSCs were irradiated with PEC-LO1 solar simulator. By keeping the active area of the cell at 19 mm\u003csup\u003e2\u003c/sup\u003e and by varying the light intensity, current-voltage (\u003cem\u003eI-V)\u003c/em\u003e data were measured with a potential scan rate of 10 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using Keithley 2400 source meter and Pecell software. The light intensity was varied by changing the distance from the solar simulator to the cells. The obtained data were used to calculate the solar cell performance parameters \u003cem\u003eJ\u003c/em\u003esc, \u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e, \u003cem\u003eff\u003c/em\u003e, and the PCE of the cell.\u003c/p\u003e \u003cp\u003eThe PCE of the cell at variable intensity levels was calculated using;\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$PCE= \\frac{{P}_{max}}{I}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({P}_{max}\\)\u003c/span\u003e\u003c/span\u003e is the maximum power output of the cell and \u003cem\u003eI\u003c/em\u003e is the irradiance of the incident light. The fill factor (\u003cem\u003eFF\u003c/em\u003e) of the cell was determined using;\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$FF= \\frac{{P}_{max}}{{V}_{OC}{J}_{SC}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eTherefore,\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$PCE= \\frac{FF {V}_{OC} {J}_{SC}}{{P}_{solar}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eEquation (\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) was used to calculate the intensity-dependent PCE values which are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Electrochemical impedance spectroscopy\u003c/h2\u003e \u003cp\u003eElectrochemical impedance spectroscopy (EIS) data of the solar cells and electrolytes were measured by a Potentiostat (Autolab PGSTAT128N) together with a frequency response analyzer (FRA) module. Impedance data were collected with NOVA 1.1 software. During the measurements, the cells were placed in a Faraday cage. The EIS measurements of solar cells were done by applying a bias voltage similar to the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e of the respective cells. To get EIS data of electrolytes, sample cells were prepared by sandwiching the electrolyte between two stainless steel electrodes. The measurement frequency window was 0.1 Hz \u0026minus;\u0026thinsp;1000 kHz and scanning was conducted with 80 steps.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results and Discussion","content":"\u003cp\u003eUnderstanding the variation in electrical conductivity of PEO-based electrolytes with temperature is crucial for optimizing electrolytes for different operating conditions. The ionic conductivities were calculated using the complex impedance data provided in Figure 2 (a). The Arrhenius equation aids in predicting conductivity trends and provides insights into the activation energy of charge carriers. The ionic conductivity obtained using complex impedance measurements is depicted in Figure 2 (b) as a function of 1000/\u003cem\u003eT\u003c/em\u003e, where \u003cem\u003eT\u003c/em\u003e represents the electrolyte temperature. The top axis of the plot in Figure 2 (b) specifies the electrolyte temperature. The electrolyte exhibits an ionic conductivity of 3.37 mS cm\u003csup\u003e-1\u003c/sup\u003e at 293.0 K, which increases to 7.31 mS cm\u003csup\u003e-1\u003c/sup\u003e at 353.0 K. The data presented in Figure 2 (b) were fitted to the following equation:\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.2\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;XRD measurements\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe XRD pattern for the 4\u003csup\u003eth\u003c/sup\u003e layer prepared with TiO\u003csub\u003e2\u003c/sub\u003e and graphene is given in Figure 03. The 2\u003cem\u003e\u0026theta;\u0026nbsp;\u003c/em\u003evalues along with relevant TiO\u003csub\u003e2\u003c/sub\u003e phases and crystal planes are marked. Most of the peaks correspond to the dominant anatase phase of TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(101, 004, 200) and the presence of several characteristic peaks in the XRD spectra provides evidence for the polycrystalline nature of the TiO\u003csub\u003e2\u003c/sub\u003e films. Peaks (110) and (101) correspond to the rutile phase of TiO\u003csub\u003e2\u003c/sub\u003e and the origin of the peak (110) FTO is due to the diffraction pattern associated with FTO glass. In comparison, (101)A, (111)R, and (200)A peaks have become broader for graphene-free samples, which can be attributed to the smaller size of crystallites or an increase in lattice defects in graphene-free samples. Furthermore, the intensity of reflection from the (004)A plane has diminished in the graphene-free sample since it is not a preferred orientation of the sample.\u003c/p\u003e\n\u003cp\u003eIn Figure 03 (a), the peak related to graphene is clearly seen at (001) crystal plane. However, the intensity of the peak is not as strong as TiO\u003csub\u003e2\u003c/sub\u003e peaks because only 0.005 g (1% w/w) of graphene has been used to fabricate the photoanode. The absence of significant carbon peaks can be due to the dominance of TiO\u003csub\u003e2\u003c/sub\u003e content (99%) in the electrode.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.3\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Raman spectroscopy\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFigure 04 shows the Raman spectra of the exfoliated graphene. Two dominant peaks are visible namely the G band and 2D band at intensities 1580 cm\u003csup\u003e-1\u003c/sup\u003e and 2730 cm\u003csup\u003e-1\u003c/sup\u003e, respectively. The occurrence of the G band is due to the stretching vibrational motion of SP\u003csup\u003e2\u003c/sup\u003e hybridization of carbon-carbon bonds, and the peak position occurs at 2730 cm\u003csup\u003e-1\u003c/sup\u003e is a characteristic signature of graphene [26].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe number of layers in exfoliated graphene was calculated using the intensity ratios between 2D and G peaks (I\u003csub\u003e2D\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e). According to the experimental results, the value obtained for I\u003csub\u003e2D\u003c/sub\u003e/I\u003csub\u003eG\u0026nbsp;\u003c/sub\u003eratio is 1.43. This data confirmed the successful synthesis of double layered graphene [26]. This exfoliated double layered graphene synthesized directly from vein graphite is used to fabricate the photoanodes of the solar cells investigated in this study.\u003c/p\u003e\n\u003cp\u003eSEM images of the fabricated photoelectrodes at a magnification of 100,000 are shown in Figure 4. Figure 4(a) shows the top surface morphology of a 4-layer photoelectrode fabricated without graphene in the 4\u003csup\u003eth\u003c/sup\u003e layer while Figure 4(b) shows the improved photoelectrode by adding graphene to the 4\u003csup\u003eth\u003c/sup\u003e layer. When comparing the morphologies of these two layers, it can be observed that 4 layered electrodes prepared by adding graphene to the 4\u003csup\u003eth\u003c/sup\u003e layer (Figure 4(b)) consist of graphene sheets. The presence of graphene in the 4\u003csup\u003eth\u003c/sup\u003e layer can enhance the conductivity in the photoelectrode and alter the dye adsorption properties as well as influence the photocurrent, PCE, and fill factor of the DSSCs. Also, the presence of graphene may minimize the charge transfer resistances at the interfaces of the TiO\u003csub\u003e2\u003c/sub\u003e layer by faster electron transport which can hinder recombination. In addition, graphene can contribute to efficiency enhancement by improving light scattering as well.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigures 4(c) and 4(d) show the top surface morphology of the two 6-layer photoelectrodes prepared without and with graphene to the 4\u003csup\u003eth\u003c/sup\u003e layer, respectively. These images confirm the formation of crack-free, nanocrystalline mesoporous thin films with high porosity that offer a large surface area for dye absorption. As we can see, these two images (Figure 4(c) and 4(d)) both look identical in the surface morphology because the same procedures and steps have been repeated to fabricate the 6\u003csup\u003eth\u003c/sup\u003e layer electrodes except for the 4\u003csup\u003eth\u003c/sup\u003e layer. The image in 4(d) confirms there are no graphene sheets visible. Therefore, the graphene in the 4\u003csup\u003eth\u003c/sup\u003e layer is well covered by the 5\u003csup\u003eth\u003c/sup\u003e and 6\u003csup\u003eth\u003c/sup\u003e TiO\u003csub\u003e2\u003c/sub\u003e layers. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.4\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Dependence of Cell Performance on Irradiance Level\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eSolar cell characteristics were evaluated as a function of intensity by taking \u003cem\u003eI\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e characteristic curves. Both graphene-added and graphene-free cells exhibited typical dye-sensitized solar cell behavior but with variations in their parameters. The plots for current density vs. cell potential (\u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e) and power density vs. cell potential (\u003cem\u003eP\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e) are shown in Figure 06. The \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e and \u003cem\u003eP\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e curves of the graphene-added DSSCs at each intensity level are given in Figures 06(a), and 06(b), respectively. The \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e and \u003cem\u003eP\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e curves of the graphene-free control DSSCs at each intensity level are shown in Figures 05 (c) and(d), respectively. The photocurrent density and output power density of both cells decrease with decreasing intensity due to the reduction of photon flux and thus resulting in low photoelectron generation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e and \u003cem\u003eP\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e characteristic curves in Figure 06 are used to determine the open-circuit voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e), the short circuit current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003esc\u003c/sub\u003e), the fill factor (\u003cem\u003eff\u003c/em\u003e), and the PCE of the fabricated DSSC under different irradiation levels. The values calculated for graphene-free DSSC (control cell) at different intensity levels are given in Table 03 while the respective values for the graphene-added cell (test cell) are given in Table 04.\u003c/p\u003e\n\u003cp\u003eThe cell fabricated without graphene in the 4\u003csup\u003eth\u003c/sup\u003e layer exhibited significantly low performance compared to that of the graphene-added cell. The fabricated DSSC without graphene achieved 5.39% of efficiency under 1108 W m\u003csup\u003e-2\u003c/sup\u003e irradiance while that in graphene added cell is 6.43%. With the gradual decrease of light irradiance level, the PCE of the cells increases though the net power output drops. This PCE increase observed in both cells with decreasing irradiance is attributed to an increase in fill factor which indicates the decrease in resistive losses (Tables 03 and 04). \u0026nbsp;For example, the PCEs of graphene-free and graphene -added cells increase from 5.05% to 6.82% under one sun illumination (1000 W m\u003csup\u003e-2\u003c/sup\u003e). Consequently, the highest PCE and \u003cem\u003eff\u003c/em\u003e are exhibited at the lowest tested irradiance level of 67 W m\u003csup\u003e-2\u003c/sup\u003e. The PCEs of graphene-free and graphene-added cells increase to 6.68% and 9.40% under 67 W m\u003csup\u003e-2\u0026nbsp;\u003c/sup\u003eintensity level. With the results obtained from both cells, it is evident that the efficiency and fill factor of the DSSCs increase with the decrease of irradiation. Achieving higher efficiencies in dye-sensitized solar cells under low light intensities agrees with the literature [\u003csup\u003e29\u003c/sup\u003e,\u003csup\u003e30\u003c/sup\u003e,\u003csup\u003e31\u003c/sup\u003e].\u003c/p\u003e\n\u003cp\u003eFurther in both the cells \u003cem\u003eff\u003c/em\u003e has increased with decreasing light intensity. It can be due to reduced, recombination kinetics, non-radiative thermalization losses and charge transport losses. At the lower intensities, the generation of electron-hole pairs in the photoelectrode is less. This decreases the probability of carrier recombination before reaching the electrodes. \u0026nbsp; Therefore, cells exhibit higher photocurrent at maximum power output contributing to a higher fill factor. At lower intensities, a smaller number of photons are available to excite electrons. Therefore, along with decreasing carrier generation and associated non-radiative recombination and thermalization of charge carriers decrease contributing to enhancing the fill factor. Since current and number charge carriers at lower light intensities are less, the resistive losses due to diffusion and the resistances are low and hence a higher fill factor can be expected.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;2: Calculated values for the\u0026nbsp;V\u003csub\u003eOC\u003c/sub\u003e,\u0026nbsp;J\u003csub\u003eSC\u003c/sub\u003e,\u0026nbsp;ff,\u0026nbsp;ŋ, and the maximum power of the cell under different irradiation levels for cells prepared without adding graphene to the 4\u003csup\u003eth\u003c/sup\u003e layer.\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"613\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eIntensity /\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eW m\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eoc\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ V\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eJ\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003esc\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003emA cm\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eopt\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ V\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eJ\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eopt\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003emA cm\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eP\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003emax\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ W\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eŋ\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eff\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e1108\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e5.39\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e69.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e1000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e5.50\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e71.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e607\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e5.94\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e71.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e381\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.02\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e72.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e251\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.29\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e74.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.33\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e76.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.35\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e78.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e104\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.48\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e78.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.59\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e80.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.68\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e81.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;3: Calculated values for the\u0026nbsp;V\u003csub\u003eOC\u003c/sub\u003e,\u0026nbsp;J\u003csub\u003eSC\u003c/sub\u003e,\u0026nbsp;ff,\u0026nbsp;ŋ, and the maximum power of the cell under different irradiation levels for cells prepared by adding graphene into the 4th layer.\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"621\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003eIntensity /\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eW m\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eoc\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ V\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eJ\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003esc\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003emA cm\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eV\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eopt\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ V\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eJ\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eopt\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003emA cm\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eP\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003emax\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ W\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eŋ\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eff\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e1108\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e17.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e15.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e6.43\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e56.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e1000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e13.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n 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\u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e8.07\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e68.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e251\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e8.41\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e71.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e8.62\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e74.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e8.79\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e76.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e104\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e9.01\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e79.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e9.23\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e81.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u003cstrong\u003e9.40\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e83.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cem\u003e4.5\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Incident photon-to-current efficiency (IPCE)\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eIPCE measurements offer valuable insight into the spectral response and performance of a DSC across the solar spectrum. By varying the wavelength of the incident light, the obtained IPCE spectrums for the two distinct variants of the fabricated solar cells are given in Figure 7. The reference solar cell is composed of a photoanode solely made of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles which provides a baseline for comparison. During characterization, it exhibits moderate IPCE values with a single narrow absorption peak. This graphene-free cell exhibits a maximum IPCE of 40.65 at 525 nm. The test cell, enhanced with graphene, shows higher IPCE with two distinctive peaks at ~345 nm and ~530 nm along with IPCE of 44.35 and 53.76%. The IPCE value is usually determined by the charge collection at the collecting electrode and dye loading capacity. With added graphene on TiO\u003csub\u003e2\u003c/sub\u003e could capture and shuttle electrons quickly to the collecting electrodes which leads to the improvement of the IPCE value of the graphene-based solar cell over the entire wavelength of the spectrum [\u003csup\u003e32\u003c/sup\u003e, \u003csup\u003e33\u003c/sup\u003e].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.6\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Electrochemical impedance (EIS) spectroscopy\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eIn order to get further insight into the higher efficiency of the test cell, EIS data is utilized. Figures 8 (a) and 8 (b) represent the Nyquist plots and Bode phase diagrams for the two cells. Using the impedance spectra Bode diagram was plotted and estimated the values of\u0026nbsp;electron transport lifetime (\u003cem\u003et\u003c/em\u003e\u003csub\u003etr\u003c/sub\u003e),\u0026nbsp;recombination lifetime (\u003cem\u003et\u003c/em\u003e\u003csub\u003erec\u003c/sub\u003e) and diffusion length (\u003cem\u003eD\u003c/em\u003e\u003csub\u003eL\u003c/sub\u003e) are given in Table 5.\u003c/p\u003e\n\u003cp\u003eThe \u003cem\u003eD\u003c/em\u003e\u003csub\u003eL\u003c/sub\u003e is the average distance traveled by a charge carrier within the semiconducting material before it recombines. This length plays a crucial role in determining the efficiency of charge carrier transport and lifetime inside the cell. In this study, \u003cem\u003eD\u003c/em\u003e\u003csub\u003eL\u003c/sub\u003e was calculated by following the equation, along with the impedance data analysis [\u003csup\u003e34\u003c/sup\u003e, \u003csup\u003e35\u003c/sup\u003e, \u003csup\u003e36\u003c/sup\u003e].\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere, \u003cem\u003eR\u003c/em\u003e\u003csub\u003etr\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003erec\u003c/sub\u003e represent the charge transfer resistance and recombination resistance. \u003cem\u003eL\u003c/em\u003e is the layer thickness [\u003csup\u003e37\u003c/sup\u003e]. Nyquist plots in Figure 8 (a) were used to determine the \u003cem\u003eR\u003c/em\u003e\u003csub\u003etr\u003c/sub\u003e and \u003cem\u003eR\u003c/em\u003e\u003csub\u003erec\u0026nbsp;\u003c/sub\u003efor each cell and layer thickness\u003cem\u003e\u0026nbsp;\u003c/em\u003ewas measured using high-resolution scanning electron microscopy (\u003cem\u003eL\u003c/em\u003e= 5.2\u0026nbsp;mm).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;4: Recombination lifetimes\u0026nbsp;(t\u003csub\u003erec\u003c/sub\u003e), electron transport lifetimes\u0026nbsp;(t\u003csub\u003etr\u003c/sub\u003e)\u0026nbsp;and diffusion lengths (D\u003csub\u003eL\u003c/sub\u003e) of the prepared DSCs.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"613\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.270358306188925%\"\u003e\n \u003cp\u003e\u003cstrong\u003eCell\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.449511400651467%\"\u003e\n \u003cp\u003e\u003cstrong\u003e(\u003cem\u003eL\u003c/em\u003e)/\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.938110749185668%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003et\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003erec\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ mS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.241042345276874%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003et\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003etr\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;/ mS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.10097719869707%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eD\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003csub\u003eL\u003c/sub\u003e\u003c/strong\u003e\u003cstrong\u003e/\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003cstrong\u003em\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.270358306188925%\"\u003e\n \u003cp\u003eDSC with TiO\u003csub\u003e2\u003c/sub\u003e/Graphene photoelectrode\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.449511400651467%\"\u003e\n \u003cp\u003e5.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.938110749185668%\"\u003e\n \u003cp\u003e3.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.241042345276874%\"\u003e\n \u003cp\u003e0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.10097719869707%\"\u003e\n \u003cp\u003e7.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"31.270358306188925%\"\u003e\n \u003cp\u003eDSC with TiO\u003csub\u003e2\u003c/sub\u003e only photoelectrode\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.449511400651467%\"\u003e\n \u003cp\u003e5.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.938110749185668%\"\u003e\n \u003cp\u003e2.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.241042345276874%\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.10097719869707%\"\u003e\n \u003cp\u003e6.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eInterestingly the study shows the DSC fabricated with TiO\u003csub\u003e2\u003c/sub\u003e and graphene has a higher diffusion length value than that of the reference cell. The increased diffusion length enhances the likelihood that the charge carriers will reach the electrodes contributing to enhancing collection efficiency. In a DSC photogenerated electrons and holes are separated at the dye-semiconductor interface. However, a certain number of charge carriers recombine instead of traveling through the external circuit, which could negatively impact the overall performance of the solar cell. By increasing the recombination lifetimes, it is possible to prolong the duration of which these electron-hole pairs remain separated. This prolonged duration allows more charge carriers to reach the electrodes and contribute to the photo-current. The study shows the fabricated solar cell with TiO\u003csub\u003e2\u003c/sub\u003e and graphene contains higher recombination lifetimes compared to the reference cell. This longer lifetime may have impacted positively to improve cell efficiency.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.7\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Effect of graphene on cell performance\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe cell fabricated by adding graphene shows higher \u003cem\u003eV\u003c/em\u003e\u003csub\u003eOC\u003c/sub\u003e, \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e, \u003cem\u003eff\u003c/em\u003e, and PCE compared to the cell without graphene. The observed performance enhancement is very likely due to the positive effects imposed by the incorporated graphene. For a better visualization of the behavior PCE and \u003cem\u003eff\u003c/em\u003e variations of the cells with light intensity are shown in Figure 9 (a) and (b) respectively. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eGraphene has excellent electrical conductivity and optical properties, enabling it to enhance the absorption of light and facilitate efficient charge transport within the solar cell, leading to higher conversion efficiencies and increased power output. The improved performance with added graphene observed in this study can be attributed to the combined effects of the following process.\u0026nbsp;\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eDecreased charge transport resistance of the photoelectrode and charge transfer resistance between two interfaces of TiO\u003csub\u003e2\u003c/sub\u003e as a result of increased conductivity [\u003csup\u003e38\u003c/sup\u003e,\u003csup\u003e39\u003c/sup\u003e]. The reduction of resistive losses improves the photocurrent of the cell. The decrease of resistive losses with added graphene is inferred by the higher \u003cem\u003eff\u0026nbsp;\u003c/em\u003eshown by the graphene-incorporated cell.\u003c/li\u003e\n \u003cli\u003eThe improved charge transfer between the FTO current collectors indirectly helps to reduce the recombination losses. The behavior is evident by the increase of \u003cem\u003eV\u003c/em\u003e\u003csub\u003eOC\u003c/sub\u003e, and \u003cem\u003eff\u0026nbsp;\u003c/em\u003eof the graphene-added cell. This process enables more efficient conversion of light energy to electricity.\u003c/li\u003e\n \u003cli\u003eThe \u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e enhancement can be contributed by faster electron extraction by graphene added interlayer from the excited dye molecules [\u003csup\u003e40\u003c/sup\u003e, \u003csup\u003e41\u003c/sup\u003e]. Graphene\u0026apos;s large surface area and high carrier mobility facilitate improved electron injection from the excited dye molecules to the Graphene/TiO\u003csub\u003e2\u0026nbsp;\u003c/sub\u003elayer, thereby enhancing the efficiency of the dye to photoelectron conversion process. This can also reduce energy loss due to non-radiative decay.\u003c/li\u003e\n \u003cli\u003eGraphene\u0026apos;s large surface area can facilitate the distribution of TiO\u003csub\u003e2\u003c/sub\u003e and thus can enhance the effective surface area available for dye adsorption by the electrode as inferred by analyzing SEM images. This promotes higher dye loading, leading to increased light absorption and improved device performance.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eFinally, it can be deduced that the DSSC made with graphene-added photoelectrode- exhibited impressive efficiency enhancement under low irradiation. For instance, the addition of 1% of graphene to the 4\u003csup\u003eth\u003c/sup\u003e TiO\u003csub\u003e2\u003c/sub\u003e layer of the photoanode improves the efficiency of the cell from 5.50% to 6.82% under one sun illumination (1000 W m\u003csup\u003e-2\u003c/sup\u003e). This is a 24% efficiency improvement. Efficiency enhancements given by the graphene-added DSSC with respect to graphene-free solar cells (control device) are given in Table 6 for different irradiance levels. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;5: Efficiency enhancements by the graphene-incorporated photo electrode-based DSSCs with respect to the graphene-free solar cell.\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"26.53061224489796%\"\u003e\n \u003cp\u003e\u003cstrong\u003eIntensity / W m\u003csup\u003e-2\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e1108\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.183673469387756%\"\u003e\n \u003cp\u003e1000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e607\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e381\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e251\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e104\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e67\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"26.53061224489796%\"\u003e\n \u003cp\u003e\u003cstrong\u003eEfficiency enhancement /%\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e19.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.183673469387756%\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e24.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e34.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e33.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e36.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e38.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e39.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e40.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.142857142857143%\"\u003e\n \u003cp\u003e40.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe present study shows that not only graphene can be used to enhance DSSC performance but also that graphene can be successfully synthesized from natural vein graphite using a scalable and cost-effective method. \u0026nbsp; \u0026nbsp;\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study reports efficiency enhancements in graphene-incorporated, quasi-solid-state DSSCs under ambient and low-light conditions. The XRD results and high-resolution SEM images confirmed the presence of anatase TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles in photoelectrodes. The Raman spectroscopy confirmed the successful fabrication of two-layer graphene from the vein graphite. One of the challenges of widely utilizing graphene in solar cells is their high cost. This study presents a cost-effective, feasible, and novel method to exfoliate vein graphite sourced directly from the mine site and a strategic way to integrate them in photoanodes. SEM images confirm the presence of graphene in the most effective layer of the photoanode.\u003c/p\u003e \u003cp\u003eThe PCEs of 5.05% graphene-free cells (control cell) increased to 6.82% with the integration of graphene into the photoanode, exhibiting 24% enhancement at ambient irradiation. The \u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e, \u003cem\u003eJ\u003c/em\u003e\u003csub\u003esc\u003c/sub\u003e, and \u003cem\u003eff\u003c/em\u003e, values of graphene-incorporated DSSC are 6.82%, 770 mV, 13.4 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, and 66.2% respectively at 1000 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Notably, the efficiency and fill factor exhibited an intriguing increase at lower light intensities. The synthesized graphene incorporated DSSC achieved a remarkable efficiency of 9.4% and a fill factor of 83.1% at 67 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e solar irradiance. The efficiency enhancement for 67 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e intensity compared to 1000 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e is \u0026sim;38%.\u003c/p\u003e \u003cp\u003eThe performance of the improved DSSC by integrating the synthesized graphene from vein graphite outperforms the reference cell at all the intensities measured. This improved efficiency is attributed to the higher charge carrier recombination lifetime (3.22 mS) and high diffusion lengths (7.1 \u0026micro;m) of the improved DSC by integrating graphene into to photoanode.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe authors would like to acknowledge the financial support from the Postgraduate Institute of Science, University of Peradeniya (grant No. PGIS/2020/10), and Peradeniya University Research Grant No. 2023/34/S.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eT.M.W.J. Conceptualization, Methodology, Project administration and Supervision, Writing, Reviewing Editing fund acquisition and Formal analysis.S.M.S.G. Data collection, Formal analysis and measurement, 1st draft preparation. G.G.D.M.G.G: Data collection, Formal analysis and measurement.B.M.K.P., Writing, Reviewing, Editing and Formal analysis. L.A.DeS.,Writing, Reviewing, Editing and Formal analysis. M.A.K.L.D. and G.R.A.K., Writing, Reviewing, Editing and Formal analysis.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to acknowledge Udara Wadasinghe in University Peradeniya, for the technical support given for this project.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMariotti, N., Bonomo, M., Fagiolari, L., Barbero, N., Gerbaldi, C., Bella, F., Barolo, C(2020)Recent advances in eco-friendly and cost-effective materials towards sustainable dye-sensitized solar cellsGreen chemistry, 22(21), 7168-7218.\u003c/li\u003e\n\u003cli\u003eMariotti, N., Bonomo, M., Fagiolari, L., Barbero, N., Gerbaldi, C., Bella, F., \u0026amp; Barolo, C(2020)Recent advances in eco-friendly and cost-effective materials towards sustainable dye-sensitized solar cellsGreen chemistry, 22(21), 7168-7218.\u003c/li\u003e\n\u003cli\u003eNishshanke, GBMMM., Arof, AK., \u0026amp; Bandara, TMWJ(2020)Review on mixed cation effect in gel polymer electrolytes for quasi solid-state dye-sensitized solar cellsIonics, 26, 3685-3704.\u003c/li\u003e\n\u003cli\u003eMu\u0026ntilde;oz-Garc\u0026iacute;a, AB., Benesperi, I., Boschloo, G., Concepcion, JJ., Delcamp, JH., Gibson, Freitag, M(2021)Dye-sensitized solar cells strike backChemical Society Reviews, 50(22), 12450-12550.\u003c/li\u003e\n\u003cli\u003eYameng Ren, Dan Zhang, Jiajia Suo, Yiming Cao, Felix TEickemeyer, Nick Vlachopoulos, Shaik MZakeeruddin, Anders Hagfeldt and Michael Gr\u0026auml;tzel., Hydroxamic acid pre-adsorption raises the efficiency of cosensitized solar cells, Nature, 2023 (613) 60\u0026ndash;65.\u003c/li\u003e\n\u003cli\u003eBandara, TMWJ., Hansadi, JMC., \u0026amp; 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Gimenez, S(2009)Electron lifetime in dye-sensitized solar cells: theory and interpretation of measurementsThe Journal of Physical Chemistry C, 113(40), 17278-17290.\u003c/li\u003e\n\u003cli\u003eBandara, TMWJ., SMSGunathilake, GBMMMNishshanke, MAKLDissanayake, NBChaure, OIOlusola, B-EMellander, MFurlani, and Ingvar Albinsson\u0026quot;Efficiency enhancement and chrono-photoelectron generation in dye-sensitized solar cells based on spin-coated TiO2 nanoparticle multilayer photoanodes and a ternary iodide gel polymer electrolyte.\u0026quot; Journal of Materials Science: Materials in Electronics 34, no28 (2023): 1969.\u003c/li\u003e\n\u003cli\u003eWang, YC., \u0026amp; Cho, CP(2017)Application of TiO2-graphene nanocomposites to photoanode of dye-sensitized solar cellJournal of Photochemistry and Photobiology A: Chemistry, 332, 1-9.\u003c/li\u003e\n\u003cli\u003eTao, E., Ma, Z., Yang, S., Li, Y., Ma, D., Xing, Z., \u0026amp; Li, Y(2020)Enhanced electrical conductivity of TiO2/graphene: The role of introducing Ca2+Journal of Alloys and Compounds, 827, 154280.\u003c/li\u003e\n\u003cli\u003eDas, S., Sudhagar, P., Kang, YS., \u0026amp; Choi, W(2014)Graphene synthesis and application for solar cellsJournal of Materials Research, 29(3), 299-319.\u003c/li\u003e\n\u003cli\u003eSu, H., \u0026amp; Hu, YH(2023)3D graphene: synthesis, properties, and solar cell applicationsChemical CommunicationsDOI https://doi.org/10.1039/D3CC01004J\u003c/li\u003e\n\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-applied-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jach","sideBox":"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)","snPcode":"10800","submissionUrl":"https://submission.nature.com/new-submission/10800/3","title":"Journal of Applied Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Graphene solar cell, Low light, Efficiency enhancement, Dye solar cells, Graphene, Multilayer Photoanode","lastPublishedDoi":"10.21203/rs.3.rs-4335227/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4335227/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGraphene is a potential candidate material to boost efficiency in solar cells. The performance of multi-layer TiO\u003csub\u003e2\u003c/sub\u003e photoanode based quasi-solid-state dye-sensitized solar cells (DSSCs) is improved by strategically integrating graphene into the appropriate layer of the photoanode. For this purpose, graphene was synthesized from vein graphite, received directly from the mine site, providing a cost-effective, feasible and new approach to enhance DSSC efficiency. Raman and XRD spectra confirm the successful exfoliation of graphite, forming graphene. Graphene integration into layers was analyzed using SEM images. The cells were constructed using photosensitized spin-coated TiO\u003csub\u003e2\u003c/sub\u003e multilayer photoanode, Pt counter-electrode, and binary salts gel-polymer electrolyte. Appreciable performance improvement was observed when graphene was added to the fourth layer of the photoanode. The quasi-solid-state DSSC without graphene demonstrated 5.50% efficiency, 700 mA open circuit voltage, 11.04 mA cm\u003csup\u003e-2 \u003c/sup\u003eshort circuit current density and 71.2% fill factor under 1000 W m\u003csup\u003e-2\u003c/sup\u003e irradiation. In contrast, the DSSC improved by graphene exhibited 6.8% efficiency, 13.4 mA cm\u003csup\u003e-2 \u003c/sup\u003eshort circuit current density, 770 mA open circuit voltage and 66.2% fill factor under 1000 Wm\u003csup\u003e-2\u003c/sup\u003e irradiation. Furthermore, the efficiency and fill factor increase were observed when the irradiance decreased. The DSSC exhibited a remarkable efficiency of 9.4% under 67 W m\u003csup\u003e-2\u003c/sup\u003e irradiance. Achieving higher efficiency for quasi-soid state configuration without relying on volatile solvent-based electrolytes is another significance of this study. The study uncovers that the strategic incorporation of graphene, synthesized in an economically viable manner, into specific layers of the photoanode significantly enhances the power conversion efficiency in DSSCs.\u003c/p\u003e","manuscriptTitle":"Strategic Integration of Graphene into Multilayer Photoanode; Enhancing Efficiency of Quasi-Solid-State Dye-Sensitized Solar Cells Under Ambient and Low Irradiance","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-07 19:12:34","doi":"10.21203/rs.3.rs-4335227/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-18T09:25:51+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-17T08:10:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281927516177820166306983491985913831425","date":"2024-08-01T06:24:24+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-10T09:10:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"89299357532423691179338369456981382151","date":"2024-06-24T03:21:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"264253012829899447668369568499271704621","date":"2024-06-21T06:03:55+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-13T05:11:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-02T09:18:52+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-29T13:07:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Electrochemistry","date":"2024-04-27T18:49:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-applied-electrochemistry","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jach","sideBox":"Learn more about [Journal of Applied Electrochemistry](http://link.springer.com/journal/10800)","snPcode":"10800","submissionUrl":"https://submission.nature.com/new-submission/10800/3","title":"Journal of Applied Electrochemistry","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"cedbcef8-21c3-4ab5-ba87-346f03b66c59","owner":[],"postedDate":"May 7th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-30T16:01:31+00:00","versionOfRecord":{"articleIdentity":"rs-4335227","link":"https://doi.org/10.1007/s10800-024-02204-x","journal":{"identity":"journal-of-applied-electrochemistry","isVorOnly":false,"title":"Journal of Applied Electrochemistry"},"publishedOn":"2024-09-23 15:57:19","publishedOnDateReadable":"September 23rd, 2024"},"versionCreatedAt":"2024-05-07 19:12:34","video":"","vorDoi":"10.1007/s10800-024-02204-x","vorDoiUrl":"https://doi.org/10.1007/s10800-024-02204-x","workflowStages":[]},"version":"v1","identity":"rs-4335227","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4335227","identity":"rs-4335227","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}