Novel Platinum-Free Counter-Electrode with PEDOT: PSS-Treated Graphite/Activated Carbon for Efficient Dye-Sensitized Solar Cells

Novel Platinum-Free Counter-Electrode with PEDOT: PSS-Treated Graphite/Activated Carbon for Efficient Dye-Sensitized Solar Cells | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Novel Platinum-Free Counter-Electrode with PEDOT: PSS-Treated Graphite/Activated Carbon for Efficient Dye-Sensitized Solar Cells G. K.R. Senadeera, R. M.S.S. Rasnayake, J. M.K.W. Kumari, P. U Sandunika, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4594353/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract Developing an efficient material as a counter electrode (CE) with excellent catalytic activity, intrinsic stability, and low cost is essential for the commercial application of dye-sensitized solar cells (DSSCs). Photovoltaic properties DSSCs fabricated with low-cost and platinum-free CEs based on different mixtures of carbon allotropes graphite (GR), activated carbon (AC) and PEDOT: PSS films. The DSSCs assembled with PEDOT: PSS/GR/AC showed an impressive photovoltaic conversion efficiency of 4.60%, compared to 4.06% for DSSCs with GR/AC CE or 1.66% for PEDOT: PSS alone or 6.56 % for Pt under the illumination 100 mW cm − 2 (AM 1.5 G) due to the superior electrocatalytic activity and the conductivity of AC and PEDOT: PSS. The fabricated carbon counter electrodes were extensively characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, cyclic voltammetry (CV), Tafel measurements and electrochemical impedance spectroscopy (EIS). The CV, EIS and Tafel measurements indicated that the PEDOT: PSS/Graphite/AC composite film has low charge-transfer resistance on the electrolyte/CE interface and high catalytic activity for the reduction of triiodide to iodide than the GR/AC CEs. It is potentially feasible that such a carbon configuration can be used as a counter electrode, replacing the more expensive Pt in DSSCs. Graphite activated carbon PEDOT:PSS counter electrode dye-sensitized solar cell Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Highlights Proposing a novel PEDOT: PSS/Graphite/Activated Carbon composite counter electrode with better performances. Achieving better interaction between the electrolyte and the counter electrode. Power conversion efficiency of 4.60 % has been found by using the PEDOT: PSS/GR/AC counter electrode 1. Introduction Among the third-generation photovoltaic devices dye-sensitized solar cells (DSSCs) are the most promising photovoltaic devices due to their desired properties such as straight forward fabrication process, environmental friendliness, and adequate efficiency [ 1 ]. A typical sandwich-structured DSSC consists of three primary components: a dye-adsorbed TiO 2 layer on a conductive glass substrate serving as the photoanode, an iodide/triiodide (I 3 − /I −) redox couple as the electrolyte, and a platinized counter electrode (CE) [ 2 ]. The CE plays a crucial role in DSSCs by collecting electrons from the external circuit and catalyzing the reduction of I 3 − to I − . This process demands both excellent catalytic activity and high conductivity from the CE materials [ 3 ]. Although platinum (Pt) and Pt-based materials are currently the standard catalysts for CEs in DSSCs due to their superior electron conductivity and catalytic efficiency. Their limited availability, high cost, and instability in iodine-based electrolytes pose significant challenges for large-scale commercial applications. Therefore, the development CEs of non-noble metal catalysts with competitive electrochemical performance and exceptional stability are essential for advancing sustainable energy technologies and facilitating their broader commercialization [ 4 ]. In recent years, a variety of alternative materials have been investigated for counter electrodes in DSSCs, aiming to achieve comparable or even superior performance to Pt at a lower cost [ 5 – 6 ]. Among them carbonaceous materials that have been successfully integrated into DSSCs include graphite [ 7 , 8 ], carbon black [ 8 , 9 ], graphene [ 10 ], carbon nanotube, activated carbon, conductive carbon [ 10 – 13 ], etc. Apart from that, conducting polymers, including polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT), exhibit good electrical conductivity and chemical stability, making them suitable for DSSC applications [ 14 , 15 ]. Among these carbonaceous materials, graphite stands out for its fascinating properties and frequent use as a catalyst and conducting layer in DSSCs, owing to its abundant availability and low cost. Natural graphite is available in three forms amorphous graphite, flake graphite, and crystalline vein graphite each possessing unique properties that suit various applications. Crystalline vein graphite, also known as Sri Lankan graphite, is particularly notable for its naturally occurring rock-like veins and high purity (over 95% pure carbon), high crystallinity, and attractive commercial demand [ 16 ]. In 1996, Kay and Gratzel (17] have presented a new type of graphite plus carbon black as a counter electrode with the overall power conversion efficiency of 6.67% under 1 sun. However, large graphite particles with low surface area exhibit very poor catalytic activity when used as counter electrode materials in DSSCs [ 18 ]. Graphitic materials, including carbon nanotubes and graphite itself, have two distinct types of planes: basal and edge planes. Basal planes are characterized by slow electron transport, while edge planes enable fast electron transport. Large graphite particles contain fewer edge planes (or more basal planes), which slows down the rate of I 3 − reduction due to high charge transfer resistance ( R CT ). This high R CT negatively impacts the fill factor (FF) and results in poor energy conversion efficiency (η) [ 17 , 18 ]. In this context, Weerappan et al have showed that submicrometer size colloidal graphite can be used as an efficient counter electrode catalyst for triiodide reduction in DSSCs and obtained an energy conversion efficiency greater than 6.0%, comparable to the conversion efficiency of Pt [ 7 ]. Low-cost carbon black with graphite counter electrode in DSSC by incorporating binders were demonstrated by Narudin et al., good adherence to the substrates with high conductivity and electrochemical activity with the overall efficiency of 5.72% was achieved with the CE fabricated with titanium (IV) isopropoxide (TTIP) [ 19 ]. Chou and colleagues demonstrated that by increasing the thickness of the graphite/carbon black film to 10.4 µm, the efficiency of DSSCs utilizing this counter electrode (CE) enhanced from 0.8–1.5% [ 20 ]. Don et al. [ 21 ] demonstrated that incorporating acetylene carbon black (AB) into graphite catalytically enhances the triiodide ion reduction in DSSCs, significantly improving photo-conversion efficiency from 3.43–5.06%. In our recent study, demonstrated that SnO 2 nanoparticles in graphite/SnO 2 composite counter electrodes enhance the adhesion of vein graphite to conducting glass substrates and increase the effective surface area of the counter electrode by creating a porous structure [ 22 ]. Apart from the graphite, Polystyrene sulfonate doped poly-(3, 4-ethylenedioxythiophene) (PEDOT: PSS), has been studied in recent past as an alternative to the Pt based counter electrodes in DSSCs [ 23 ]. This is mainly due to its good electrical conductivity, electro catalytic activity, and good ability to form homogenous CEs. Koji Kitamura and Seimei Shiratori demonstrated that layer-by-layer self-assembled mesoporous PEDOT–PSS and carbon black hybrid films can serve as effective platinum-free counter electrodes for DSSCs, achieving 4.7% efficiency, just 8% lower than devices using conventional thermally deposited platinum on fluorine-doped tin oxide glass counter electrodes [ 24 ]. Muto et al [ 25 ] reported printable mesoporous counter electrodes using pastes containing PEDOT–PSS solution, TiO 2 nanoparticles, and indium–tin oxide nanoparticles, achieving an efficiency of 4.38%, which is approximately 20% less than the 5.41% efficiency yielded by Pt counter electrodes. Shunjian Xu et al have developed a nanoporous composite film of TiO 2 /SnO 2 and PEDOT: PSS as a counter electrode for DSSCs, achieving a 6.54% efficiency, which is 36.5% higher than that of a cell using a pristine PEDOT: PSS film [ 26 ]. By considering above factors, in the present study Sri Lankan graphite was used as the major component to fabricate low-cost CEs for DSSCs. Due to the poor adherence properties of this vain graphite on to the conducting substrate, here trace amount of Titanium isopropoxide was used in combination with activated carbon aiming to improve the adhesive properties with enhanced catalytic and electrical conductivity of the CE. The composition of the graphite to activated carbon CE was optimized by investigating the current –voltage characteristics of the DSSCs. In order to future enhance the photovoltaic characteristic of the devices, incorporation of PEDOT: PSS was carried out in the above combination in different ways. It was observed that, DSSCs fabricated with PEDOT:PSS/GR/AC counter electrodes with TiO 2 binder gives superior photovoltaic properties than the GR/AC CEs and comparative with the traditional expensive Pt counter electrode in DSSCs. 2. Experimental details 2.1. Materials Sri Lankan natural vein graphite collected from “ Bogala ” mines was used as the starting material for graphite. To prepare the photoanodes, Ruthenium N719 dye (RuL2(NCS)2:2TBA, Solaronix), titanium dioxide P-90 powder (Evonik), titanium dioxide P-25 powder (Degussa), polyethylene glycol (PEG 2000, Merck), triton X-100 (Merck), hydrochloric acid (37%, Merck) and α-terpineol (Sigma-Aldrich) were used as received without further purification. To prepare the electrolyte, iodine chips (I 2 ), acetonitrile (anhydrous), ethylene carbonate and propylene carbonate, were purchased from Sigma-Aldrich. Fluorine doped tin oxide (FTO) conducting glasses (8 Ω/sq, Solaronix) were used as the substrates for both photoanode and counter electrodes. 2.2. Photo-anode preparation A photo-anodes with two layers of TiO 2 on a FTO substrates were prepared by following a procedure reported previously [ 23 ]. In brief, for the first compact TiO 2 layer of P90, 0.25 g of P90 TiO 2 powder was ground with 1 ml of 0.1 M HNO 3 in an agate mortar for 20 minutes. The resulting paste was then spin-coated onto a pre clean FTO glass substrate at 3000 rpm for 60 seconds. The FTO substrate with P90 TiO 2 was then sintered at 450°C for 45 minutes. After cooling to room temperature, the second layer of mesoporous TiO 2 was prepared by using P25 TiO 2 powder. 0.25 g of TiO 2 powder (P90) was mixed with 1 ml of 0.1 M HNO 3 and ground in a mortar and pestle. Then 0.02 g of Triton X-100 and 0.05 g of PEG 2000 were added as binders and mixed thoroughly until the mixture formed a creamy paste. This paste was doctor-bladed onto the previously prepared first P90 TiO 2 compact layer over a 0.25 cm 2 cell area. Then the substrate with two types of films were sintered at 450°C for 45 minutes to obtain a photoanode with porous TiO 2 layer on top. Finally, these photoanodes were dipped independently in ethanolic dye solution containing 0.3 mM of N719 dye at room temperature for 24 h. 2.3 Preparation of Counter electrode The counter electrodes were prepared using Sri Lankan natural vein graphite (GR) flakes sourced from the Bogala mines in Sri Lanka. The powdered graphite samples were obtained by following the method outlined by Kumara et al [ 27 ]. Specifically, the graphite flakes were subjected to ball milling for 20 minutes, followed by sieving to achieve particles smaller than 63 µm. These particles were then dispersed in deionized water with continuous stirring and subsequently agitated for approximately 1 hour. The resulting graphite layer that formed on the water surface was collected onto a glass slide and vacuum dried for approximately 12 hours. The carbon content of the resulting buoyant graphite powder was analyzed using ASTM-561 methodology and by measuring the residue's weight. The analysis indicated a total carbon content of 99.94%, confirming the high purity of the graphite [ 20 ]. The counter electrodes with different amounts of graphite and activated carbon powder were fabricated and tested by varying the amount of activated carbon powder purchased from (Aldrich). The best performances in the DSSCs were obtained with the following compositions and further studied were carried out with the same composition. The CEs with best composition was fabricated by using 0.875 g of aforementioned graphite powder and 0.0375g of active carbon powder and mixed well with 1 ml α-terpineol, 100 µl Titanium (IV) isopropoxide (TTIP) and 10 µl Glacial acetic acid (GAA) in an agate mortar for 30 min until homogeneous mixture is formed. Then creamy paste was doctor bladed on pre cleaned FTO glass substrate and subjected to annealed at 400 °C for 25 minutes. 2.4 Fabrication of PEDOT PSS in-cooperated counter electrode PEDOT: PSS (Baytron, Bayer AG, ϭ = 8 × 10 − 2 S/cm) was utilized as the starting material. Ethanoic solutions were prepared by mixing absolute ethanol and the PEDOT: PSS solution in a 1:1 volume ratio. Different amounts of this solution was spin coated as follows. At first, this solutions were spin coated at 1500 rpm for 1 min on pre cleaned FTO and FTO/Graphite/AC and then sintered at 80 °C, and 450 °C for 20 min . 2.5 Preparation of Liquid electrolyte The iodide/triiodide-based liquid electrolyte for this study was prepared by dissolving 0.738 g of tetrapropylammonium iodide (Pr 4 NI), 0.06 g of iodine (I 2 ), and 3.6 ml of molten ethylene carbonate (EC) in 1 ml of acetonitrile. The resulting solution was magnetically stirred for 24 hours at ambient temperature. 2.6. Fabrication of DSSCs and their characterization DSSCs were fabricated by placing the liquid electrolyte between the TiO 2 photoanode and the counter electrodes. The active surface area of the device is 0.25 cm 2 . The current density–voltage ( J-V ) characteristics of the DSSCs were measured using a computer-controlled, calibrated solar simulator (Oriel Newport LCS-100) connected to a Potentiostat/Galvanostat (Metrohm Autolab PGSTAT 128 N) under AM 1.5 illumination (100 mW cm −2 ). A Xenon 100 W lamp with an AM 1.5 filter (400 nm- 1100 nm) Class A with spectral Match of 0.75–1.25 was used to obtain the simulated sunlight with above intensity. In order to compare the performance of DSSCs with graphite based and Pt based counter electrodes, DSSCs with the identical TiO 2 photoanode with the same electrolyte were also fabricated using Pt CEs. Impedance measurements of DSSCs were taken using a Potentiostat/Galvanostat (Metrohm Autolab PGSTAT 128 N) with Frequency Response Analyzer (Metrohm Autolab FRA 32) covering the frequency range from 0.01 Hz to1.0 MHz. These solar cell measurements were also performed under 100 mW cm −2 illumination. 2.7 Characterization of Photoanode and the counter electrode The surface morphology of the photoanodes and counter electrodes were characterized by scanning electron microscopy (SEM) using Zeiss EVO LS15 scanning electron microscope and by transmission electron microscopy (TEM) using JEOL JEM 2100 transmission electron microscope, respectively. The wide-angle X-ray spectroscopy (WAXS) was performed using Rigaku X-ray diffractometer with CuKα radiation (λ = 1.5406 Å). The diffuse reflection spectra were obtained in the wavelength range from 240 to 800 nm using UV-Vis spectrophotometer (Shimadzu 2450) with an integrating sphere attachment. Impedance measurements of DSSCs were taken using a Potentiostat/Galvanostat (Metrohm Autolab PGSTAT 128 N) with Frequency Response Analyzer (Metrohm Autolab FRA 32) covering the frequency range from 0.01 Hz to1.0 MHz. These solar cell measurements were also performed under 100 mW cm − 2 illumination. In order to study the electrocatalytic properties of the counter electrode, cyclic voltammetry (CV) experiments were done at a scan rate of 50 mV s − 1 by using a three-electrode set up having a Pt wire counter electrode, Ag/AgCl reference electrode and Pt or FTO/GR/AC based composite CEs with and without PEDOT:PSS. A solution of acetonitrile prepared with 10 mM LiI, 0.1 M LiClO 4 , and 1 mM I 2 was used as supporting electrolyte. The Tafel polarization and electrochemical impedance spectroscopy (EIS) measurements of counter electrodes were carried out for symmetrical dummy cells composed of the same CE materials (Pt, pristine graphite and PEDOT: PSSS/graphite/AC/composite) on both electrodes with active cell area of 1.0 cm 2 . The liquid electrolyte that used to fabricate DSSCs was sandwiched in between the identical counter electrodes for taking Tafel polarization and EIS measurements. 3. Results and Discussion Figure 1 shows the scanning electron microcopy (SEM) images of the top view and the cross sectional views of the TiO 2 photoanodes. The photoanode made with P25 nanoparticles has a fairly uniform distribution of TiO 2 nanoparticles of average size around 20 nm as expected. The cross sectional view of the photoanodes showed a uniform, thicker film with approximately ~ 11.28 µm thickness. Figure 2 (a) shows the surface morphology of the pristine graphite, which lacks the porous structure necessary for effective electrolyte diffusion. This characteristic hinders the efficiency of the iodide/triiodide redox reaction at the counter electrode. The SEM photograph showing surface morphology of the graphite/activated carbon CE is shown in the Fig. 2 (b). The graphite and activated carbon as well as the TiO 2 crystallite are fairly uniformly distributed without cracks in the surface. The size of the TiO 2 particles formed by TTIP in Graphite/AC was found to be relatively smaller at a particle size of approximately ~ 30– 40 nm. Figure 2 (c) shows the top view SEM of the composite counter electrode fabricated with PEDOT: PSSS. It shows that a porous coating with wide cracks. As it is observed by Veerappan et al [07] on the surface morphologies of graphite-based materials in their counter electrodes, it can be concluded that in these PEDOT PSS treated CE has more edge planes, i.e., a higher number of catalytic sites than the other counter electrode [ 28 ]. Figure 3 shows cross-sectional SEM images of (a) GR/AC and (b) PEDOT: PSS/GR/AC. The optimal thickness of the GR/AC counter electrode was determined by testing DSSCs with counter electrodes of different thicknesses. As can be seen from the Fig. 3 (a) the optimum thickness was approximately ~ 15.32 µm. Slight increase in the film thickness (~ 16.00 µm) was observed with the incorporation of PEDOT:PSS layer on the FTO with the optimized composition. The average crystallite size of the GR/AC crystallite is around 500–600 nm. In the production of GR/AC CEs, the GR/AC connectivity and compactness are critical for improving hole extraction and lowering contact resistance in solar cells. As shown in Fig. 2 (b) and 3(a), large graphite flakes are bound to each other and well packed probably due to the formation of TiO 2 binder and the presence of the activated carbon with high porosity. Graphite flakes provide good electronic conductivity for the GR/AC CEs, while the activated carbon nanoparticles act as conductive fillers and bridge the gaps among the graphite flakes. Typically, high-porosity carbon films naturally exhibit unique properties, including a large surface area and excellent conductivity. These characteristics are advantageous for electron collection, charge transfer, and ion diffusion. [ 29 ]. Furthermore, the high porosity can create more active sites, enhancing I - /I 3 - electro catalytic activity. The porous structure shown in Fig. 3 (b) is likely facilitate the diffusion of I 3 - ions to the active sites for reduction. This structure improves the interconnected network on the carbon material surface, resulting in strong adhesion of the electrodes to the FTO substrate, which is beneficial for long-term stability. Similar phenomenon was observed by Don et al [ 30 ] in their counter electrodes fabricated with carbon black/TiO 2 CEs as well as the hydrophilic carbon/TiO 2 colloid composite counter electrodes fabricated by Kouhnavard et al respectively [ 31 ]. Raman spectroscopy is a valuable method for analyzing the structure and quality of carbon materials. It is particularly effective in identifying defects and the ordered or disordered nature of carbon nanomaterials. Figure 4 shows the Raman spectra of the GR/AC and PEDOT: PSS/GR/AC counter electrodes. Two distinct peaks are evident at ~ 1353 cm⁻¹ and ~ 1596 cm⁻¹, corresponding to the D and G bands of the carbon materials, respectively [ 32 , 33 ]. The D band is commonly linked to amorphous carbon and partial disordering of the sp² domain, while the G band corresponds to the E2g vibrational mode of the sp² hexagonal network plane [ 33 ]. Therefore, analyzing the peak intensity ratio of the D to G bands allows for the assessment of the quality of the deposited carbon material. Interestingly, while defective carbon is undesirable for transparent conductive films and device applications, it is advantageous for dye-sensitized solar cells (DSSCs) and supercapacitors, as it provides sites that enhance catalytic activity [ 34 ]. The calculated Raman peak ratio (I D /I G ) values are tabulated in Table 1 . The larger I D /I G ratios obtained for graphite/Activated carbon with PEDOT: PSS indicates the significant amount of structural defects present in these materials resulting better electrocatalytic activity. As mentioned by Lee et al defects are advantageous for producing an effective catalytic activity [ 35 ]. Table 1 Calculated Raman ratio (I D /I G ) values for (a) Gr/AC composite CE, (b) PEDOT: PSS Coated Gr/AC composite CE Counter Electrode D- band (cm -1 ) G-band (cm -1 ) I D /I G A (GR/AC) 1355 1596 0.92 B (PEDOT:PSS/GR/AC 1354 1596 0.95 Figure 5 (a) and 5(b) shows the XRD spectrum of GR/AC and PEDOT:PSS/GR/AC composites. Here, the presence of narrow and sharp diffraction peak which is centered at ~ 26.6° corresponds to the oriented crystal plane (002) of hexagonal graphite. In addition, less intense peaks at, 54.7 ° (004) suggests the presence of graphite in the material [ 35 ]. The XRD pattern shows both anatase and rutile peaks belongs to TiO 2 which has formed due to the incorporation of TTIP as the binder in the fabrication of counter electrode. Week peaks belong to anatase and rutile phases of TiO 2 at 33.67 (101), 37.1 (004) 51.57 (200), 61.58 (204) and 65.50 (002) can be clearly seen in the figure. Similar peak positions were observed by Xiaoyan Pan in his study on TiO 2 /graphite photocatalytic composite [ 36 ]. In order to see efficiency variation of the DSSCs with GR/AC counter electrode with different film thickness and the sintering temperature of the composite, DSSCs were fabricated with different thick CEs and also with the different sintering temperatures of them. Since it is not possible to fabricate uniform homogeneous films on the FTO substrate with good adhesive properties, film thickness was varied with two different thickness only. Figure 6 shows the efficiency variation of the DSSCs fabricated with different CE fabricated under different thickness and sintering temperatures. Extracted photovoltaic parameters from the J-V characteristic curves for DSSCs with different CS sintered at various temperatures are tabulated in Table 2 . As can be seen from Fig. 6 and Table 2 , the efficiency increase with increasing sintering temperature up to 400 °C and then decrease. DSSCs fabricated with CEs using two scotch tapes (3m) thickness showed better solar cells efficiencies than the three tapes thickness. As observed from SEM the best CE film thickness found to be 15.32 µm as depicted in Fig. 2 (a). This is mainly attributed with the adhesive properties of the material to the FTO as well as the formation of non-uniform CE with higher film thickness than this. It was observed that when DSCS were fabricated with the liquid electrolyte, CEs with thicker films trend to peel off from the FTO substrate. Table 2 shows the photovoltaic parameters extracted from the current voltage characteristics of the DSSC with different CEs sintered at various temperatures. As can be seen from the table GR/AC counter electrode sintered at 400 °C showed the highest efficiency of 4.06% whereas the DSSCS with Pt CE showed 6.56% efficiency. The photovoltaic parameters of the DSSCs fabricated with different thickness and sintered at 400 °C are tabulated in Table 3 . It can be seen that DSSCs fabricated with CEs with two tapes thickness shows higher photovoltaic parameters than the thicker films. Due to poor adherence and also duet to the difficulty in preparing homogeneous CEs with less than two tapes thickness we have varied the CE thickness with two and three tapes only. In order to check the reproducibility of all these devices, eight DSSCs were tested in each composition and deviations of photovoltaic properties are indicated as in the tables. Table 2 Photovoltaic parameters extracted from the current voltage characteristics of the DSSCs with different CEs sintered at various temperatures Counter electrode Sintered Temperature (° C) J SC ( mA cm −2 ) V OC (mV) FF% Eff% GA/AC Not Sintered 5.24 ± 0.02 796.74 ± 0.65 53.51 ± 0.15 2.23 ± 0.05 100 7.10 ± 0.05 801.93 ± 0.05 52.78 ± 0.25 2.99 ± 0.15 200 7.79 ± 0.33 796.44 ± 0.45 53.79 ± 0.14 3.32 ± 0.28 300 8.28 ± 0.06 792.16 ± 0.55 56.66 ± 0.16 3.71 ± 0.14 400 11.60 ± 0.25 744.31± 0.75 57.59 ± 0.35 4.06 ± 0.03 500 7.31 ± 0.36 798.27 ± 0.12 58.96± 0.25 3.43 ± 0.15 Pt Not Sintered 13.34 ± 0.15 770.90 ± 0.85 63.99± 0.05 6.56 ± 0.04 Table 3 Photovoltaic parameters of DSSCs fabricated with different thick counter electrodes sintered at 400 °C. Counter Electrode Thickness J SC (mA cm −2 ) V OC (mV) FF% Eff% GR/AC 3 tapes 7.64 ± 0.25 804.68 ± 0.16 56.85 ± 0.03 3.49 ± 0.25 GR/AC 2 tapes 11.60 ± 0.25 744.31 ± 0.75 57.59 ± 0.35 4.06 ± 0.05 Pt 13.34 ± 0.15 770.90 ± 0.85 63.99 ± 0.05 6.56 ± 0.04 Figure 7 shows the current-voltage characteristic of DSSCs fabricated with different CEs including the PEDOT: PSS composite. The photovoltaic parameters are summarized in the Table 4 . As it is evident from the table due to adhesive problems of the PEDOT: PSS to the FTO substrate, DSSCs fabricated with pristine PEDOT: PSS showed poor performances with 1.66% efficiency. However, the DSSCs fabricated with GA/AC incorporated CE showed slightly higher efficiency of 4.60% than the DSSCs with only GR/AC counter electrode. Table 4 Solar cell performance of DSSCs fabricated with different counter electrodes Counter electrode J SC ( mA cm -2 ) V OC ( mV) FF% Eff% Only PEDOT:PSS 10.20 ± 0.01 620.20 ± 0.02 25.82 ± 0.03 1.66 ± 0.02 GA/AC 11.60 ± 0.25 744.31 ± 0.75 57.59 ± 0.35 4.06 ± 0.05 PEDOT:PSS/GA/AC 13.23 ± 0.03 702.20 ± 0.01 59.64 ± 0.02 4.60 ± 0.12 Pt 13.34 ± 0.15 770.90 ± 0.85 63.99 ± 0.05 6.56 ± 0.04 Electrochemical impedance spectroscopy (EIS) and equivalent circuit modeling are standard methods for estimating the internal resistance of DSSCs. Within DSSCs, charge carrier transport from the photoanode to the counter electrode encounters several resistive components. These include the series resistance ( R S ), which encompasses the sheet resistance of the fluorine-doped tin oxide (FTO) glass and the contact resistance of the cell; the resistance at the FTO/TiO 2 interface (R FTO–TiO2 ); the electron transport resistance within the TiO 2 film ( R TiO2 ); the charge-transfer resistance associated with electron recombination in the TiO 2 film and I 3 − ions in the electrolyte ( R CT ); the Warburg impedance representing the Nernstian diffusion of I 3 − ions in the electrolyte ( Z d ); the charge-transfer resistance at the counter electrode/electrolyte interface ( R CE–electrolyte ); and the charge-transfer resistance at the exposed FTO/electrolyte interface ( R FTO–electrolyte ). In DSSCs, the charge-transfer resistance at the counter electrode/electrolyte interface ( R CE–electrolyte ) is typically the most significant among these resistive elements. Consequently, R CT often refers specifically to R CE–electrolyte unless otherwise specified. Among these resistances, the series resistance (R S ) and the charge-transfer resistance at the counter electrode/electrolyte interface ( R CT ) are critically dependent on the counter electrode properties [ 3 , 8 , 7 , 37 ]. Specially the R CT value influences the number of electrons that get transferred from CE to the electrolyte to complete the DSSC circuit. To evaluate the catalytic behavior of the graphitic/AC and PEDOT: PSS incorporated CEs, the charge transfers resistances and sheet resistances of the symmetric cells were measured using EIS. Figure 8 shows the Nyquist plot for both Pt and graphite/AC and PEDOT: PSSS/GR/AC symmetric cells. The R CT and sheet resistance ( R S ) were determined through equivalent circuit fitting and calculated values are tabulated in Table 5 . As it can be seen from the table the series resistance ( R S ) with PEDOT:PSS/GR/AC and GR/AC electrodes are 33.72 Ω and 50.08 Ω respectively. Both values are higher than the R S value of the Pt electrode (10.9 Ω ) This may be due to the lower conductivities of the carbon based electrodes. On the other hand, as it was observed by Murakami et al, this could be possibly due to the larger thickness and the rougher GR/AC film surfaces [ 8 ]. A lower R S corresponds to a higher conductivity of the counter electrode and a better filling factor of the DSSC which is consistent with our FF values depicted in the Table 4 for the Pt CE [ 37 ]. Therefore, the DSSC with GR/AC CE showed lower values for the FF, J SC , and lower efficiency than the DSSCs with Pt CE [ 7 , 8 ]. The charge transfer resistance R 1CT or R CE–electrolyte is an important parameter associated with charge transfer across the electrolyte/CE interface. As expected, the lowest R 1CT value of 6.55 Ω shown in Table 4 corresponds to the Pt/electrolyte interface. The GR/AC/electrolyte interface shows much higher R 1CT value of 118.4 Ω compared to the Pt/electrolyte interface. This is very likely caused by the higher resistivity of the nanoporous GR/AC composite compared to Pt. The R 1CT value of PEDOT: PSS incorporated CE based DSSCs is 84.06 Ω and it is much lower than the DSSCs with GR/AC counter electrode but much higher than that of the DSSCs with Pt CE. Normally, a decreasing trend in R 1CT value is associated with an increasing trend in J SC for most of the DSSC systems studied as can be observed in this study too [ 36 ]. The higher efficiency in DSSCs with PEDOT: PSS composite mainly results from higher catalytic activity which is assigned to faster diffusion of redox couple in the electrolyte as observed by the Wu et al [ 38 ]. Incorporation of PEDOT: PSS in GR/AC counter electrode results in higher performance which mainly arises from the higher J SC . The enhanced J SC is mainly results from higher electro catalytic activity owing to lower R CT and diffusion resistance which is in line with the above morphological and electrochemical analysis [ 39 ]. Table 5 Series resistance ( R S ) and the the charge transfer resistance R 1CT ( R CE–electrolyte values of DSSCS with different CEs Counter Electrode R S (Ω) R 1CT (Ω) GR/AC 50.08 ± 0.25 118.24 ± 0.42 PEDOT:PSS/GR/AC 33.72 ± 0.18 84.06 ± 0.31 Pt 10.60 ± 0.32 9.11 ± 0.23 Cyclic voltammetry (CV) analysis is an important and efficient tool for analyzing ion diffusivity and the catalytic mechanism acting in an electrochemical system [ 40 ]. The cyclic voltammetry analysis for electrodes was carried out by a three-electrode system. Figure 9 shows the cyclic voltamograms of Pt, Graphite /AC and PEDOT: PSS/GR/AC electrode, in which the potential ranged from − 0.2 to 1.2 V (vs. Ag/AgCl) at the scan rate of 50 mV s − 1 . Two pairs of redox peaks were observed in the cyclic voltammograms of all the CEs. The relative negative pair was assigned to the redox reaction as in Eq. (1) and the positive one was assigned to the redox reaction in Eq. (2) [ 41 ]. I 3 − + 2e − ⇌ 3I − ----------------(1) 3I + 2e − → 2I ----------------(2) In DSSCs, the reduction reaction of triiodide (I 3 − ) occurs at the counter electrode, which is crucial for completing the circuit and regenerating the dye molecules. Therefore, it is essential to study the redox behavior of the iodide/triiodide (I − /I 3 − ) couple at negative potentials [ 42 ]. It has been reported that the electrocatalytic performance of a counter electrode for the reduction of I 3 − in DSSCs is related to the cathodic peak current observed at more negative potentials. A higher cathodic peak current density indicates better catalytic activity of the counter electrode [ 42 , 43 , 44 ]. Apart from the as peak current density, counter electrode catalytic ability is estimated using peak to peak separation (ΔE pp ) of the oxidative and reduction peaks [ 42 ]. The peak to peak separation is calculated from Eq. (3). A higher cathodic peak current density indicates better catalytic activity of the counter electrode [ 41 – 45 ]. Δ E pp = | E p (anodic) – E p (cathodic)| -------------(3) Table 6 shows the estimated electrochemical parameters including the |ΔE pp | and the diffusion coefficient values of different counter electrodes obtained from CV measurements. Table 6 Electrochemical parameters of different counter electrodes obtained from CV Measurements Counter electrode | J OX1 | (mA cm -2 ) | J RED1 | ( mA cm -2 ) | J OX1 |/ | J RED1 | | ΔE pp | (V) D n (x10 -4 )/cm 2 s -1 PEDOT:PSS/GR/AC 2.98 2.85 1.05 0.02 14.21 GR/AC 1.34 1.04 1.29 0.22 1.89 Pt 0.60 0.49 1.22 0.13 0.42 The reduction current peaks (cathodic peak) of the PEDOT: PSS/GR/AC electrode were much higher than that of the both Pt and the GR/AC electrodes. On the other hand, the reduction peak currents density of GR/AC based electrodes was also much greater than that of the Pt counter electrode. This could be attributed to the large active surface area of both the GR/AC and PEDOT: PSS/GR/AC electrodes. The higher the cathodic peak current density, better the catalytic activity of the counter electrode [ 46 ]. Moreover, the | J OX1 | / | J RED1 | ratio is a parameter which is important in estimating the reversibility of the I − /I 3 − redox reaction [ 47 ]. The value of | J OX1 | / | J RED1 | for the PEDOT: PSS/GR/AC is much closer to 1.00 than the corresponding values for the GR/AC CE, or even for the Pt cathode, suggesting that the reversible redox reaction I − → I 3 − is more stable on the PEDOT:PSS/GR/AC electrode than on the Pt electrode and the GR/AC electrode [ 47 ]. Based on the cyclic voltammetry results, the incorporation of PEDOT: PSS improves the catalytic activity of the composite CE. Similar behavior of these parameters was also observed by Wu et al in their studies on polyoxometalate-doped polypyrrole film electrodes [ 47 ] as well as by Duan et al with metal selenide alloy CEs in DSSCs [ 48 ]. For a real DSSC device, a higher reversibility implies the rapid conversion of I 3 ¯ into I ¯ species for dye recovery. Therefore, more N719 molecules can excite electrons for electricity generation as observed with the highest J SC in DSSCs fabricated with PEDOT: PSS/GR/AC counter electrode. The correlation among peak current density ( J RED1 ), diffusion coefficient ( D n ) and scan rate (ⱱ) can be expressed by the Randles-Sevcik Eq. 5. J RED1 = KAC n 1.5 D n 0.5 ⱱ 0.5 ---------------- (5) Where K is a constant (= 2.69 x 10 5 ) n is the number of electrodes contributing to charge transfer, A is the electrode area and C represents the bulk concentration of redox species [ 49 , 50 ]. Tafel polarization of all three counter electrodes were performed to further analyze the charge transfer kinetics at the interface of CE/electrolyte using a symmetric cell configuration. The polarization curves display the logarithmic current density as depicted in the Fig. 10 . In the equilibrium state, the electron transfer rate can be determined from the intersection of the linear cathodic and anodic branches of the curves, which indicates the exchange current density ( J O ) [ 51 ]. The J ₀ is an essential indicator of the catalytic activity of the counter electrode. This is used to assess its effectiveness in reducing iodide ions. A higher J ₀ value denotes greater catalytic activity of the counter electrode for iodide ion reduction [ 52 ]. J 0 is inversely proportional to R CT with the following equation. J O = RT / nFR CT , where R is the gas constant, T is the absolute temperature, F is the Faraday’s constant and R CT is the charge transfer resistance [ 52 ]. Furthermore, the limiting diffusion current density ( J lim ), corresponding to the intersection of the cathodic branch with the Y-axis, is a parameter directly proportional to the diffusion coefficient ( D n ) of the I⁻/I₃⁻ redox couple at the CE/electrolyte interface. This parameter can be used to estimate the diffusion performance of the redox couples. The highest J lim demonstrates the faster diffusion rate of the I 3 − reduction in the electrolyte. The trends of J lim would consistent with the Jo for all CEs. The exchange current density ( J ₀) can be calculated from the polarization region, while J lim can be measured from the diffusion region. The D n value is directly proportional to diffusion coefficient ( D n ) of the I − / I 3 − redox couple at the CE/Electrolyte interface [ 53 ]. D n = L (J Lim ) / 2nFC), where D is the diffusion coefficient of I 3 ¯ , l is the thickness of diffusion layer, C is the concentration of I 3 ¯ [ 54 ]. Estimated J O values and J LIM values are tabulated in the Table 7 . Table 7 Electrochemical parameters of different electrodes extracted from EIS measurements and Tafel plot measurements. Counter electrode log J O ( mA cm -2 ) log J lim ( mA cm -2 ) GR/AC 0.85 1.60 PEDOT:PSS/GR/AC 1.04 1.73 Pt 1.84 1.95 The J 0 value of the cells with GR/AC, PEDOT:PSS/GR/AC and Pt electrode are approximately 0.85 mA cm −2 and 1.04 mA cm −2 and 1.84 mA cm −2 respectively. This indicates that the PEDOT: PSS/GR/AC CEs in the DSSCs can handle the back reaction more efficiently than the GR/AC counter electrode, and contribute toward improving the current in the device as observed in the J sc values depicted in the Table 3 . However, the low values of J O than the Pt CE indicates the lower conductivity in comparison with that of the Pt CEs. Figure 12 and Table 7 , J lim follows the same order as J 0 . In summary, according to the systematic evaluation of electrocatalytic activity for the PEDOT: PSS/GR/AC counter electrode, it is as effective and sufficient as Pt to catalyze the reduction reaction of triiodide to iodide. Similar results for the J o and J lim values of the Pt electrodes were observed by several authors like Wei et al [ 55 ] and Yue et al [ 56 ]. Figure 6 and Table 1 , J lim follows the same order as J 0 . As shown in the Table 7 , the J lim values lie in the order of Pt > PEDOT:PSS/GR/AC > GR/AC, indicating that PEDOT:PSS/GR/AC can effectively catalyze the reduction of I 3 − and reduce the concentration near the electrode surface due to its high catalytic ability, thereby accelerating the diffusion rate of redox to the electrode surface [ 51 , 52 ]. Therefore, the photovoltaic performance of the DSSCs, in agreement with results obtained in CV, EIS and Tafel measurements. Hence, from this study one can conclude that PEDOT: PSS/GR/AC composite CE has a great ability to trigger the reduction of triiodide ions at the electrolyte/CE interface though it cannot outperform the Pt CE. In summary, according to the systematic evaluation and study of electrocatalytic activity for the PEDOT: PSS/GR/AC counter electrode, it is as effective and sufficient as Pt to catalyze the reduction reaction of triiodide to iodide. 5. Conclusions In this study, we developed a novel three-component composite carbon counter electrode (tri-carbon) utilizing Sri Lankan vain graphite, activated carbon and PEDOT: PSS, which can be used to improve the electrochemical performance of graphite. The integration of activated carbon and PEDOT into the graphite matrix reduced charge transfer resistance, leading to an increase in JSC and consequently improved electrocatalytic activity and charge transport, as evidenced by EIS and Tafel measurements. The tri-carbon counter electrode demonstrated superior charge transfer properties and catalytic ability due to the synergistic effects of charge transfer kinetics, catalytic properties of I 3 ¯, and electrical conductivity. DSSCs assembled with the tri-carbon counter electrode, GR/AC, and Pt counter electrode with Ru N719 dye-sensitized photoanodes achieved efficiencies of 4.60%, 4.0%, and 6.05% respectively. Our results indicate that the composite materials incorporating PEDOT have significant potential for DSSC applications and warrant further investigation. Declarations Author Contribution G.K.R. Senadeera and P. Ekanayake were responsible for funding acquisition, resources, conceptualization, and writing the original draft. Formal analysis, investigation, data curation, and visualization were carried out by R.M.S.S. Rasnayake, J.M.K.W. Kumari, P.U. Sandunika, D.L.N. Jayathilaka, and T. Jaseetharan. Methodology, validation, project administration, and supervision were managed by G.K.R. Senadeera, M.A.K.L. Dissanayaka, and P. Ekanayake. All authors contributed to validation, reviewed the manuscript, and agreed to its publication. 6. Acknowledgment The authors gratefully acknowledge the Open University of Sri Lanka, National Institute of Fundamental Studies, Sri Lanka and the Universiti Brunei Darussalam for providing necessary financial assistance and the infrastructure facility. 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Senadeera","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsklEQVRIiWNgGAWjYDACHhBRAeU8OEC0ljNQTgLRWhjbSNEi73P84ePCeTaJDeyHHzAknCGsg8HwbI+x8cxtaYkNPGkGDAk3iNHSz8MmzbvtcGIDQw7QYR+I0sL+/DfvHKAW/jdEapHnbTBj5m0AapEA2UKMwwx4zhhL8xxLM26TeGZwgCjvy/ekP/zMU2Mj28+f/PDBh2PE2HIAymAD4gO41SHb0kCUslEwCkbBKBjRAAC5ljZAe+XVGAAAAABJRU5ErkJggg==","orcid":"","institution":"Open University of Sri Lanka","correspondingAuthor":true,"prefix":"","firstName":"G.","middleName":"K.R.","lastName":"Senadeera","suffix":""},{"id":324320390,"identity":"71332611-ee04-409a-9a09-470bb20d0aef","order_by":1,"name":"R. M.S.S. Rasnayake","email":"","orcid":"","institution":"Open University of Sri Lanka","correspondingAuthor":false,"prefix":"","firstName":"R.","middleName":"M.S.S.","lastName":"Rasnayake","suffix":""},{"id":324320391,"identity":"cba8852d-019b-48b1-9ac2-582e91d3c2f2","order_by":2,"name":"J. M.K.W. Kumari","email":"","orcid":"","institution":"National Institute of Fundamental Studies","correspondingAuthor":false,"prefix":"","firstName":"J.","middleName":"M.K.W.","lastName":"Kumari","suffix":""},{"id":324320394,"identity":"e34a307b-ac25-4a2f-8860-2081ad883b0b","order_by":3,"name":"P. U Sandunika","email":"","orcid":"","institution":"National Institute of Fundamental Studies","correspondingAuthor":false,"prefix":"","firstName":"P.","middleName":"U","lastName":"Sandunika","suffix":""},{"id":324320395,"identity":"3a518982-2221-4be5-a96c-7e7ff8d564b6","order_by":4,"name":"M. A.K.L. Dissanayaka","email":"","orcid":"","institution":"National Institute of Fundamental Studies","correspondingAuthor":false,"prefix":"","firstName":"M.","middleName":"A.K.L.","lastName":"Dissanayaka","suffix":""},{"id":324320397,"identity":"ce2a98ec-4a9f-481e-bb6a-188fe1aa7afa","order_by":5,"name":"D. L.N. Jayathilaka","email":"","orcid":"","institution":"Open University of Sri Lanka","correspondingAuthor":false,"prefix":"","firstName":"D.","middleName":"L.N.","lastName":"Jayathilaka","suffix":""},{"id":324320399,"identity":"efff3b03-89dc-4449-afcb-918df6c37e0a","order_by":6,"name":"T. Jaseetharan","email":"","orcid":"","institution":"South Eastern University of Sri Lanka","correspondingAuthor":false,"prefix":"","firstName":"T.","middleName":"","lastName":"Jaseetharan","suffix":""},{"id":324320400,"identity":"80dfbabb-fa4d-471c-b725-7829ceeaa022","order_by":7,"name":"P. Ekanayake","email":"","orcid":"","institution":"Universiti Brunei Darussalam","correspondingAuthor":false,"prefix":"","firstName":"P.","middleName":"","lastName":"Ekanayake","suffix":""}],"badges":[],"createdAt":"2024-06-17 13:14:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4594353/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4594353/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":60601325,"identity":"82d7e6fc-2e3d-48ca-a441-bbe909dc0b5e","added_by":"auto","created_at":"2024-07-18 16:05:02","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":89553,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron micrographs of TiO\u003csub\u003e2\u003c/sub\u003e photoanode (a) top view and (b) cross sectional view.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/f33f229ac2238aef7f52d6ec.jpg"},{"id":60602308,"identity":"cae913fe-c3a5-4a4b-ab72-eb2ba8e6a6b3","added_by":"auto","created_at":"2024-07-18 16:13:02","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":93617,"visible":true,"origin":"","legend":"\u003cp\u003eThe top-view SEM images of (a) graphite ( b) graphite/AC and (c) /PEDOT:PSS/ graphite/AC\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/6e7b95a2e607aae5ffcbbf46.jpg"},{"id":60601323,"identity":"b1bfcb14-019b-460d-937f-5bb7a17797c6","added_by":"auto","created_at":"2024-07-18 16:05:02","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":92398,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional SEM images of (a) graphite /AC and (b) PEDOT: PSS/graphite/AC\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/4d830ff5fe1faa7d72f01de6.jpg"},{"id":60601322,"identity":"c05c0538-9922-447f-b5b5-3e449b34644c","added_by":"auto","created_at":"2024-07-18 16:05:02","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":44825,"visible":true,"origin":"","legend":"\u003cp\u003eRaman spectroscopy of (a)Gr/AC composite CE, (b) PEDOT: PSS Coated Gr/AC composite CE\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/6e1495713dd899aa22f9394b.jpg"},{"id":60601327,"identity":"37b08b53-87a3-4382-8712-890d7f40a32f","added_by":"auto","created_at":"2024-07-18 16:05:02","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":49569,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of two different composites: Graphite/AC and PEDOT:PSS/GR/AC\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/927fe6fd4c2a4a53936bcefa.jpg"},{"id":60602309,"identity":"5d8ea8e9-9044-444e-80f2-25973e5e740f","added_by":"auto","created_at":"2024-07-18 16:13:02","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":39854,"visible":true,"origin":"","legend":"\u003cp\u003eEfficiency variation of DSCS with two different thick GR/AC counted electrode sintered at different temperatures.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/626d1e86da4a85b15a83feec.jpg"},{"id":60603051,"identity":"afe6d209-1f29-4286-a107-03e74c22053a","added_by":"auto","created_at":"2024-07-18 16:21:03","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":61813,"visible":true,"origin":"","legend":"\u003cp\u003ethe Current-voltage characteristic of DSSCs fabricated with different CEs including the PEDOT: PSS composite\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/bcc9cb14b755d91b6921af1b.jpg"},{"id":60601328,"identity":"73b949d1-5d2f-40c0-95ee-870f5ed9b48e","added_by":"auto","created_at":"2024-07-18 16:05:03","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":39595,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plot for both Pt and graphite/Ac and PEDOT:PSSS/GR/AC symmetric cells\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/2fc86507ddacf16b5f3d9212.jpg"},{"id":60602312,"identity":"280f1509-876e-4d1e-86bd-92fe1bd4f46d","added_by":"auto","created_at":"2024-07-18 16:13:03","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":68940,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms of (a) Pt, (b) Gr/AC and (c) PEDOT: PSS/GR/AC counter electrodes.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/794d83705635d1dd925db7cc.jpg"},{"id":60603913,"identity":"9ee03f9a-87f5-446b-b959-f9ade5d9b355","added_by":"auto","created_at":"2024-07-18 16:29:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1421080,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/6896f8c4-7c93-4c22-8da1-0375fb5d28d4.pdf"},{"id":60601331,"identity":"52762d71-076f-4eb6-ab5b-0166cfbdfae0","added_by":"auto","created_at":"2024-07-18 16:05:03","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":91748,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/a408d49c1b9c030c42a198f0.jpg"},{"id":60601329,"identity":"8521cfa9-d16e-4616-bc59-888cc6a434da","added_by":"auto","created_at":"2024-07-18 16:05:03","extension":"jpg","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":91748,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4594353/v1/a82a4b4e839f2daff1f1caed.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Novel Platinum-Free Counter-Electrode with PEDOT: PSS-Treated Graphite/Activated Carbon for Efficient Dye-Sensitized Solar Cells","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eProposing a novel PEDOT: PSS/Graphite/Activated Carbon composite counter electrode with better performances.\u003c/li\u003e\n \u003cli\u003eAchieving better interaction between the electrolyte and the counter electrode.\u003c/li\u003e\n \u003cli\u003ePower conversion efficiency of 4.60 % has been found by using the PEDOT: PSS/GR/AC counter electrode\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eAmong the third-generation photovoltaic devices dye-sensitized solar cells (DSSCs) are the most promising photovoltaic devices due to their desired properties such as straight forward fabrication process, environmental friendliness, and adequate efficiency [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. A typical sandwich-structured DSSC consists of three primary components: a dye-adsorbed TiO\u003csub\u003e2\u003c/sub\u003e layer on a conductive glass substrate serving as the photoanode, an iodide/triiodide (I\u003csub\u003e3\u003c/sub\u003e \u003csup\u003e\u0026minus;\u003c/sup\u003e/I \u003csup\u003e\u0026minus;)\u003c/sup\u003e redox couple as the electrolyte, and a platinized counter electrode (CE) [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The CE plays a crucial role in DSSCs by collecting electrons from the external circuit and catalyzing the reduction of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e to I\u003csup\u003e\u0026minus;\u003c/sup\u003e. This process demands both excellent catalytic activity and high conductivity from the CE materials [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Although platinum (Pt) and Pt-based materials are currently the standard catalysts for CEs in DSSCs due to their superior electron conductivity and catalytic efficiency. Their limited availability, high cost, and instability in iodine-based electrolytes pose significant challenges for large-scale commercial applications. Therefore, the development CEs of non-noble metal catalysts with competitive electrochemical performance and exceptional stability are essential for advancing sustainable energy technologies and facilitating their broader commercialization [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. In recent years, a variety of alternative materials have been investigated for counter electrodes in DSSCs, aiming to achieve comparable or even superior performance to Pt at a lower cost [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Among them carbonaceous materials that have been successfully integrated into DSSCs include graphite [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], carbon black [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], graphene [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], carbon nanotube, activated carbon, conductive carbon [\u003cspan additionalcitationids=\"CR11 CR12\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], etc. Apart from that, conducting polymers, including polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT), exhibit good electrical conductivity and chemical stability, making them suitable for DSSC applications [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Among these carbonaceous materials, graphite stands out for its fascinating properties and frequent use as a catalyst and conducting layer in DSSCs, owing to its abundant availability and low cost. Natural graphite is available in three forms amorphous graphite, flake graphite, and crystalline vein graphite each possessing unique properties that suit various applications. Crystalline vein graphite, also known as Sri Lankan graphite, is particularly notable for its naturally occurring rock-like veins and high purity (over 95% pure carbon), high crystallinity, and attractive commercial demand [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In 1996, Kay and Gratzel (17] have presented a new type of graphite plus carbon black as a counter electrode with the overall power conversion efficiency of 6.67% under 1 sun. However, large graphite particles with low surface area exhibit very poor catalytic activity when used as counter electrode materials in DSSCs [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Graphitic materials, including carbon nanotubes and graphite itself, have two distinct types of planes: basal and edge planes. Basal planes are characterized by slow electron transport, while edge planes enable fast electron transport. Large graphite particles contain fewer edge planes (or more basal planes), which slows down the rate of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e reduction due to high charge transfer resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e). This high \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e negatively impacts the fill factor (FF) and results in poor energy conversion efficiency (η) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In this context, Weerappan et al have showed that submicrometer size colloidal graphite can be used as an efficient counter electrode catalyst for triiodide reduction in DSSCs and obtained an energy conversion efficiency greater than 6.0%, comparable to the conversion efficiency of Pt [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Low-cost carbon black with graphite counter electrode in DSSC by incorporating binders were demonstrated by Narudin et al., good adherence to the substrates with high conductivity and electrochemical activity with the overall efficiency of 5.72% was achieved with the CE fabricated with titanium (IV) isopropoxide (TTIP) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Chou and colleagues demonstrated that by increasing the thickness of the graphite/carbon black film to 10.4 \u0026micro;m, the efficiency of DSSCs utilizing this counter electrode (CE) enhanced from 0.8\u0026ndash;1.5% [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Don et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] demonstrated that incorporating acetylene carbon black (AB) into graphite catalytically enhances the triiodide ion reduction in DSSCs, significantly improving photo-conversion efficiency from 3.43\u0026ndash;5.06%. In our recent study, demonstrated that SnO\u003csub\u003e2\u003c/sub\u003e nanoparticles in graphite/SnO\u003csub\u003e2\u003c/sub\u003e composite counter electrodes enhance the adhesion of vein graphite to conducting glass substrates and increase the effective surface area of the counter electrode by creating a porous structure [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Apart from the graphite, Polystyrene sulfonate doped poly-(3, 4-ethylenedioxythiophene) (PEDOT: PSS), has been studied in recent past as an alternative to the Pt based counter electrodes in DSSCs [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. This is mainly due to its good electrical conductivity, electro catalytic activity, and good ability to form homogenous CEs. Koji Kitamura and Seimei Shiratori demonstrated that layer-by-layer self-assembled mesoporous PEDOT\u0026ndash;PSS and carbon black hybrid films can serve as effective platinum-free counter electrodes for DSSCs, achieving 4.7% efficiency, just 8% lower than devices using conventional thermally deposited platinum on fluorine-doped tin oxide glass counter electrodes [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Muto et al [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] reported printable mesoporous counter electrodes using pastes containing PEDOT\u0026ndash;PSS solution, TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles, and indium\u0026ndash;tin oxide nanoparticles, achieving an efficiency of 4.38%, which is approximately 20% less than the 5.41% efficiency yielded by Pt counter electrodes. Shunjian Xu et al have developed a nanoporous composite film of TiO\u003csub\u003e2\u003c/sub\u003e/SnO\u003csub\u003e2\u003c/sub\u003e and PEDOT: PSS as a counter electrode for DSSCs, achieving a 6.54% efficiency, which is 36.5% higher than that of a cell using a pristine PEDOT: PSS film [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. By considering above factors, in the present study Sri Lankan graphite was used as the major component to fabricate low-cost CEs for DSSCs. Due to the poor adherence properties of this vain graphite on to the conducting substrate, here trace amount of Titanium isopropoxide was used in combination with activated carbon aiming to improve the adhesive properties with enhanced catalytic and electrical conductivity of the CE. The composition of the graphite to activated carbon CE was optimized by investigating the current \u0026ndash;voltage characteristics of the DSSCs. In order to future enhance the photovoltaic characteristic of the devices, incorporation of PEDOT: PSS was carried out in the above combination in different ways. It was observed that, DSSCs fabricated with PEDOT:PSS/GR/AC counter electrodes with TiO\u003csub\u003e2\u003c/sub\u003e binder gives superior photovoltaic properties than the GR/AC CEs and comparative with the traditional expensive Pt counter electrode in DSSCs.\u003c/p\u003e"},{"header":"2. Experimental details","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eSri Lankan natural vein graphite collected from \u0026ldquo;\u003cem\u003eBogala\u003c/em\u003e\u0026rdquo; mines was used as the starting material for graphite. To prepare the photoanodes, Ruthenium N719 dye (RuL2(NCS)2:2TBA, Solaronix), titanium dioxide P-90 powder (Evonik), titanium dioxide P-25 powder (Degussa), polyethylene glycol (PEG 2000, Merck), triton X-100 (Merck), hydrochloric acid (37%, Merck) and α-terpineol (Sigma-Aldrich) were used as received without further purification. To prepare the electrolyte, iodine chips (I\u003csub\u003e2\u003c/sub\u003e), acetonitrile (anhydrous), ethylene carbonate and propylene carbonate, were purchased from Sigma-Aldrich. Fluorine doped tin oxide (FTO) conducting glasses (8 Ω/sq, Solaronix) were used as the substrates for both photoanode and counter electrodes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Photo-anode preparation\u003c/h2\u003e \u003cp\u003eA photo-anodes with two layers of TiO\u003csub\u003e2\u003c/sub\u003e on a FTO substrates were prepared by following a procedure reported previously [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. In brief, for the first compact TiO\u003csub\u003e2\u003c/sub\u003e layer of P90, 0.25 g of P90 TiO\u003csub\u003e2\u003c/sub\u003e powder was ground with 1 ml of 0.1 M HNO\u003csub\u003e3\u003c/sub\u003e in an agate mortar for 20 minutes. The resulting paste was then spin-coated onto a pre clean FTO glass substrate at 3000 rpm for 60 seconds. The FTO substrate with P90 TiO\u003csub\u003e2\u003c/sub\u003e was then sintered at 450\u0026deg;C for 45 minutes. After cooling to room temperature, the second layer of mesoporous TiO\u003csub\u003e2\u003c/sub\u003e was prepared by using P25 TiO\u003csub\u003e2\u003c/sub\u003e powder. 0.25 g of TiO\u003csub\u003e2\u003c/sub\u003e powder (P90) was mixed with 1 ml of 0.1 M HNO\u003csub\u003e3\u003c/sub\u003e and ground in a mortar and pestle. Then 0.02 g of Triton X-100 and 0.05 g of PEG 2000 were added as binders and mixed thoroughly until the mixture formed a creamy paste. This paste was doctor-bladed onto the previously prepared first P90 TiO\u003csub\u003e2\u003c/sub\u003e compact layer over a 0.25 cm\u003csup\u003e2\u003c/sup\u003e cell area. Then the substrate with two types of films were sintered at 450\u0026deg;C for 45 minutes to obtain a photoanode with porous TiO\u003csub\u003e2\u003c/sub\u003e layer on top. Finally, these photoanodes were dipped independently in ethanolic dye solution containing 0.3 mM of N719 dye at room temperature for 24 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation of Counter electrode\u003c/h2\u003e \u003cp\u003eThe counter electrodes were prepared using Sri Lankan natural vein graphite (GR) flakes sourced from the \u003cem\u003eBogala\u003c/em\u003e mines in Sri Lanka. The powdered graphite samples were obtained by following the method outlined by Kumara et al [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Specifically, the graphite flakes were subjected to ball milling for 20 minutes, followed by sieving to achieve particles smaller than 63 \u0026micro;m. These particles were then dispersed in deionized water with continuous stirring and subsequently agitated for approximately 1 hour. The resulting graphite layer that formed on the water surface was collected onto a glass slide and vacuum dried for approximately 12 hours. The carbon content of the resulting buoyant graphite powder was analyzed using ASTM-561 methodology and by measuring the residue's weight. The analysis indicated a total carbon content of 99.94%, confirming the high purity of the graphite [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The counter electrodes with different amounts of graphite and activated carbon powder were fabricated and tested by varying the amount of activated carbon powder purchased from (Aldrich). The best performances in the DSSCs were obtained with the following compositions and further studied were carried out with the same composition. The CEs with best composition was fabricated by using 0.875 g of aforementioned graphite powder and 0.0375g of active carbon powder and mixed well with 1 ml α-terpineol, 100 \u0026micro;l Titanium (IV) isopropoxide (TTIP) and 10 \u0026micro;l Glacial acetic acid (GAA) in an agate mortar for 30 min until homogeneous mixture is formed. Then creamy paste was doctor bladed on pre cleaned FTO glass substrate and subjected to annealed at 400 \u0026deg;C for 25 minutes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Fabrication of PEDOT PSS in-cooperated counter electrode\u003c/h2\u003e \u003cp\u003ePEDOT: PSS (Baytron, Bayer AG, ϭ = 8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e S/cm) was utilized as the starting material. Ethanoic solutions were prepared by mixing absolute ethanol and the PEDOT: PSS solution in a 1:1 volume ratio. Different amounts of this solution was spin coated as follows. At first, this solutions were spin coated at 1500 rpm for 1 min on pre cleaned FTO and FTO/Graphite/AC and then sintered at 80 \u0026deg;C, and 450 \u0026deg;C for 20 min .\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Preparation of Liquid electrolyte\u003c/h2\u003e \u003cp\u003eThe iodide/triiodide-based liquid electrolyte for this study was prepared by dissolving 0.738 g of tetrapropylammonium iodide (Pr\u003csub\u003e4\u003c/sub\u003eNI), 0.06 g of iodine (I\u003csub\u003e2\u003c/sub\u003e), and 3.6 ml of molten ethylene carbonate (EC) in 1 ml of acetonitrile. The resulting solution was magnetically stirred for 24 hours at ambient temperature.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Fabrication of DSSCs and their characterization\u003c/h2\u003e \u003cp\u003eDSSCs were fabricated by placing the liquid electrolyte between the TiO\u003csub\u003e2\u003c/sub\u003e photoanode and the counter electrodes. The active surface area of the device is 0.25 cm\u003csup\u003e2\u003c/sup\u003e. The current density\u0026ndash;voltage (\u003cem\u003eJ-V\u003c/em\u003e) characteristics of the DSSCs were measured using a computer-controlled, calibrated solar simulator (Oriel Newport LCS-100) connected to a Potentiostat/Galvanostat (Metrohm Autolab PGSTAT 128 N) under AM 1.5 illumination (100 mW cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e). A Xenon 100 W lamp with an AM 1.5 filter (400 nm- 1100 nm) Class A with spectral Match of 0.75\u0026ndash;1.25 was used to obtain the simulated sunlight with above intensity. In order to compare the performance of DSSCs with graphite based and Pt based counter electrodes, DSSCs with the identical TiO\u003csub\u003e2\u003c/sub\u003e photoanode with the same electrolyte were also fabricated using Pt CEs. Impedance measurements of DSSCs were taken using a Potentiostat/Galvanostat (Metrohm Autolab PGSTAT 128 N) with Frequency Response Analyzer (Metrohm Autolab FRA 32) covering the frequency range from 0.01 Hz to1.0 MHz. These solar cell measurements were also performed under 100 mW cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e illumination.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Characterization of Photoanode and the counter electrode\u003c/h2\u003e \u003cp\u003eThe surface morphology of the photoanodes and counter electrodes were characterized by scanning electron microscopy (SEM) using Zeiss EVO LS15 scanning electron microscope and by transmission electron microscopy (TEM) using JEOL JEM 2100 transmission electron microscope, respectively. The wide-angle X-ray spectroscopy (WAXS) was performed using Rigaku X-ray diffractometer with CuKα radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;). The diffuse reflection spectra were obtained in the wavelength range from 240 to 800 nm using UV-Vis spectrophotometer (Shimadzu 2450) with an integrating sphere attachment. Impedance measurements of DSSCs were taken using a Potentiostat/Galvanostat (Metrohm Autolab PGSTAT 128 N) with Frequency Response Analyzer (Metrohm Autolab FRA 32) covering the frequency range from 0.01 Hz to1.0 MHz. These solar cell measurements were also performed under 100 mW cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e illumination. In order to study the electrocatalytic properties of the counter electrode, cyclic voltammetry (CV) experiments were done at a scan rate of 50 mV s \u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e by using a three-electrode set up having a Pt wire counter electrode, Ag/AgCl reference electrode and Pt or FTO/GR/AC based composite CEs with and without PEDOT:PSS. A solution of acetonitrile prepared with 10 mM LiI, 0.1 M LiClO\u003csub\u003e4\u003c/sub\u003e, and 1 mM I\u003csub\u003e2\u003c/sub\u003e was used as supporting electrolyte. The Tafel polarization and electrochemical impedance spectroscopy (EIS) measurements of counter electrodes were carried out for symmetrical dummy cells composed of the same CE materials (Pt, pristine graphite and PEDOT: PSSS/graphite/AC/composite) on both electrodes with active cell area of 1.0 cm\u003csup\u003e2\u003c/sup\u003e. The liquid electrolyte that used to fabricate DSSCs was sandwiched in between the identical counter electrodes for taking Tafel polarization and EIS measurements.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the scanning electron microcopy (SEM) images of the top view and the cross sectional views of the TiO\u003csub\u003e2\u003c/sub\u003e photoanodes. The photoanode made with P25 nanoparticles has a fairly uniform distribution of TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles of average size around 20 nm as expected. The cross sectional view of the photoanodes showed a uniform, thicker film with approximately\u0026thinsp;~\u0026thinsp;11.28 \u0026micro;m thickness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) shows the surface morphology of the pristine graphite, which lacks the porous structure necessary for effective electrolyte diffusion. This characteristic hinders the efficiency of the iodide/triiodide redox reaction at the counter electrode. The SEM photograph showing surface morphology of the graphite/activated carbon CE is shown in the Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). The graphite and activated carbon as well as the TiO\u003csub\u003e2\u003c/sub\u003e crystallite are fairly uniformly distributed without cracks in the surface. The size of the TiO\u003csub\u003e2\u003c/sub\u003e particles formed by TTIP in Graphite/AC was found to be relatively smaller at a particle size of approximately\u0026thinsp;~\u0026thinsp;30\u0026ndash; 40 nm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (c) shows the top view SEM of the composite counter electrode fabricated with PEDOT: PSSS. It shows that a porous coating with wide cracks. As it is observed by Veerappan et al [07] on the surface morphologies of graphite-based materials in their counter electrodes, it can be concluded that in these PEDOT PSS treated CE has more edge planes, i.e., a higher number of catalytic sites than the other counter electrode [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows cross-sectional SEM images of (a) GR/AC and (b) PEDOT: PSS/GR/AC. The optimal thickness of the GR/AC counter electrode was determined by testing DSSCs with counter electrodes of different thicknesses. As can be seen from the Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e (a) the optimum thickness was approximately\u0026thinsp;~\u0026thinsp;15.32 \u0026micro;m. Slight increase in the film thickness (~\u0026thinsp;16.00 \u0026micro;m) was observed with the incorporation of PEDOT:PSS layer on the FTO with the optimized composition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe average crystallite size of the GR/AC crystallite is around 500\u0026ndash;600 nm. In the production of GR/AC CEs, the GR/AC connectivity and compactness are critical for improving hole extraction and lowering contact resistance in solar cells. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) and 3(a), large graphite flakes are bound to each other and well packed probably due to the formation of TiO\u003csub\u003e2\u003c/sub\u003e binder and the presence of the activated carbon with high porosity. Graphite flakes provide good electronic conductivity for the GR/AC CEs, while the activated carbon nanoparticles act as conductive fillers and bridge the gaps among the graphite flakes. Typically, high-porosity carbon films naturally exhibit unique properties, including a large surface area and excellent conductivity. These characteristics are advantageous for electron collection, charge transfer, and ion diffusion. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Furthermore, the high porosity can create more active sites, enhancing I\u003csup\u003e-\u003c/sup\u003e/I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e electro catalytic activity. The porous structure shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) is likely facilitate the diffusion of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e ions to the active sites for reduction. This structure improves the interconnected network on the carbon material surface, resulting in strong adhesion of the electrodes to the FTO substrate, which is beneficial for long-term stability. Similar phenomenon was observed by Don et al [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] in their counter electrodes fabricated with carbon black/TiO\u003csub\u003e2\u003c/sub\u003e CEs as well as the hydrophilic carbon/TiO\u003csub\u003e2\u003c/sub\u003e colloid composite counter electrodes fabricated by Kouhnavard et al respectively [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRaman spectroscopy is a valuable method for analyzing the structure and quality of carbon materials. It is particularly effective in identifying defects and the ordered or disordered nature of carbon nanomaterials. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the Raman spectra of the GR/AC and PEDOT: PSS/GR/AC counter electrodes. Two distinct peaks are evident at ~\u0026thinsp;1353 cm⁻\u0026sup1; and ~\u0026thinsp;1596 cm⁻\u0026sup1;, corresponding to the D and G bands of the carbon materials, respectively [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The D band is commonly linked to amorphous carbon and partial disordering of the sp\u0026sup2; domain, while the G band corresponds to the E2g vibrational mode of the sp\u0026sup2; hexagonal network plane [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Therefore, analyzing the peak intensity ratio of the D to G bands allows for the assessment of the quality of the deposited carbon material. Interestingly, while defective carbon is undesirable for transparent conductive films and device applications, it is advantageous for dye-sensitized solar cells (DSSCs) and supercapacitors, as it provides sites that enhance catalytic activity [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe calculated Raman peak ratio (I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e) values are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The larger I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratios obtained for graphite/Activated carbon with PEDOT: PSS indicates the significant amount of structural defects present in these materials resulting better electrocatalytic activity. As mentioned by Lee et al defects are advantageous for producing an effective catalytic activity [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculated Raman ratio (I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ) values for (a) Gr/AC composite CE, (b) PEDOT: PSS Coated Gr/AC composite CE\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter Electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD- band (cm\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eG-band (cm\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eI\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA (GR/AC)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1355\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.92\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eB (PEDOT:PSS/GR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1354\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a) and 5(b) shows the XRD spectrum of GR/AC and PEDOT:PSS/GR/AC composites. Here, the presence of narrow and sharp diffraction peak which is centered at ~\u0026thinsp;26.6\u0026deg; corresponds to the oriented crystal plane (002) of hexagonal graphite. In addition, less intense peaks at, 54.7 \u0026deg; (004) suggests the presence of graphite in the material [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The XRD pattern shows both anatase and rutile peaks belongs to TiO\u003csub\u003e2\u003c/sub\u003e which has formed due to the incorporation of TTIP as the binder in the fabrication of counter electrode. Week peaks belong to anatase and rutile phases of TiO\u003csub\u003e2\u003c/sub\u003e at 33.67 (101), 37.1 (004) 51.57 (200), 61.58 (204) and 65.50 (002) can be clearly seen in the figure. Similar peak positions were observed by Xiaoyan Pan in his study on TiO\u003csub\u003e2\u003c/sub\u003e/graphite photocatalytic composite [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to see efficiency variation of the DSSCs with GR/AC counter electrode with different film thickness and the sintering temperature of the composite, DSSCs were fabricated with different thick CEs and also with the different sintering temperatures of them. Since it is not possible to fabricate uniform homogeneous films on the FTO substrate with good adhesive properties, film thickness was varied with two different thickness only. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the efficiency variation of the DSSCs fabricated with different CE fabricated under different thickness and sintering temperatures. Extracted photovoltaic parameters from the \u003cem\u003eJ-V\u003c/em\u003e characteristic curves for DSSCs with different CS sintered at various temperatures are tabulated in Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the efficiency increase with increasing sintering temperature up to 400 \u0026deg;C and then decrease. DSSCs fabricated with CEs using two scotch tapes (3m) thickness showed better solar cells efficiencies than the three tapes thickness. As observed from SEM the best CE film thickness found to be 15.32 \u0026micro;m as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a). This is mainly attributed with the adhesive properties of the material to the FTO as well as the formation of non-uniform CE with higher film thickness than this. It was observed that when DSCS were fabricated with the liquid electrolyte, CEs with thicker films trend to peel off from the FTO substrate. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the photovoltaic parameters extracted from the current voltage characteristics of the DSSC with different CEs sintered at various temperatures. As can be seen from the table GR/AC counter electrode sintered at 400 \u0026deg;C showed the highest efficiency of 4.06% whereas the DSSCS with Pt CE showed 6.56% efficiency. The photovoltaic parameters of the DSSCs fabricated with different thickness and sintered at 400 \u0026deg;C are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It can be seen that DSSCs fabricated with CEs with two tapes thickness shows higher photovoltaic parameters than the thicker films. Due to poor adherence and also duet to the difficulty in preparing homogeneous CEs with less than two tapes thickness we have varied the CE thickness with two and three tapes only. In order to check the reproducibility of all these devices, eight DSSCs were tested in each composition and deviations of photovoltaic properties are indicated as in the tables.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhotovoltaic parameters extracted from the current voltage characteristics of the DSSCs with different CEs sintered at various temperatures\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSintered Temperature (\u0026deg; C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e( mA cm \u003csup\u003e\u0026minus;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eV\u003c/em\u003e\u003csub\u003eOC\u003c/sub\u003e (mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFF%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEff%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e \u003cp\u003eGA/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNot Sintered\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e5.24 \u0026plusmn; 0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e796.74 \u0026plusmn; 0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e53.51 \u0026plusmn; 0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.23 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.10 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e801.93 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e52.78 \u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e2.99 \u0026plusmn; 0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.79 \u0026plusmn; 0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e796.44 \u0026plusmn; 0.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e53.79 \u0026plusmn; 0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e3.32 \u0026plusmn; 0.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e8.28 \u0026plusmn; 0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e792.16 \u0026plusmn; 0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e56.66 \u0026plusmn; 0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e3.71 \u0026plusmn; 0.14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e400\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e11.60 \u0026plusmn; 0.25\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e744.31\u0026plusmn; 0.75\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e57.59 \u0026plusmn; 0.35\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e4.06 \u0026plusmn; 0.03\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.31 \u0026plusmn; 0.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e798.27 \u0026plusmn; 0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e58.96\u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e3.43 \u0026plusmn; 0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNot Sintered\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e13.34 \u0026plusmn; 0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e770.90 \u0026plusmn; 0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e63.99\u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e6.56 \u0026plusmn; 0.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhotovoltaic parameters of DSSCs fabricated with different thick counter electrodes sintered at 400 \u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter Electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThickness\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(mA cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eV\u003c/em\u003e\u003csub\u003eOC\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFF%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEff%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3 tapes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.64 \u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e804.68 \u0026plusmn; 0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e56.85 \u0026plusmn; 0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e3.49 \u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 tapes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e11.60 \u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e744.31 \u0026plusmn; 0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e57.59 \u0026plusmn; 0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e4.06 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e13.34 \u0026plusmn; 0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e770.90 \u0026plusmn; 0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e63.99 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e6.56 \u0026plusmn; 0.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the current-voltage characteristic of DSSCs fabricated with different CEs including the PEDOT: PSS composite. The photovoltaic parameters are summarized in the Table \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. As it is evident from the table due to adhesive problems of the PEDOT: PSS to the FTO substrate, DSSCs fabricated with pristine PEDOT: PSS showed poor performances with 1.66% efficiency. However, the DSSCs fabricated with GA/AC incorporated CE showed slightly higher efficiency of 4.60% than the DSSCs with only GR/AC counter electrode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSolar cell performance of DSSCs fabricated with different counter electrodes\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e ( mA cm\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eV\u003c/em\u003e\u003csub\u003eOC\u003c/sub\u003e ( mV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFF%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eEff%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOnly PEDOT:PSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.20 \u0026plusmn; 0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e620.20 \u0026plusmn; 0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e25.82 \u0026plusmn; 0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e1.66 \u0026plusmn; 0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGA/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e11.60 \u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e744.31 \u0026plusmn; 0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e57.59 \u0026plusmn; 0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4.06 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePEDOT:PSS/GA/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e13.23 \u0026plusmn; 0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e702.20 \u0026plusmn; 0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e59.64 \u0026plusmn; 0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4.60 \u0026plusmn; 0.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e13.34 \u0026plusmn; 0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e770.90 \u0026plusmn; 0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e63.99 \u0026plusmn; 0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e6.56 \u0026plusmn; 0.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eElectrochemical impedance spectroscopy (EIS) and equivalent circuit modeling are standard methods for estimating the internal resistance of DSSCs. Within DSSCs, charge carrier transport from the photoanode to the counter electrode encounters several resistive components. These include the series resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e), which encompasses the sheet resistance of the fluorine-doped tin oxide (FTO) glass and the contact resistance of the cell; the resistance at the FTO/TiO\u003csub\u003e2\u003c/sub\u003e interface (R\u003csub\u003eFTO\u0026ndash;TiO2\u003c/sub\u003e); the electron transport resistance within the TiO\u003csub\u003e2\u003c/sub\u003e film (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eTiO2\u003c/sub\u003e); the charge-transfer resistance associated with electron recombination in the TiO\u003csub\u003e2\u003c/sub\u003e film and I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e ions in the electrolyte (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e); the Warburg impedance representing the Nernstian diffusion of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e ions in the electrolyte (\u003cem\u003eZ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e); the charge-transfer resistance at the counter electrode/electrolyte interface (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eCE\u0026ndash;electrolyte\u003c/sub\u003e); and the charge-transfer resistance at the exposed FTO/electrolyte interface (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eFTO\u0026ndash;electrolyte\u003c/sub\u003e). In DSSCs, the charge-transfer resistance at the counter electrode/electrolyte interface (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eCE\u0026ndash;electrolyte\u003c/sub\u003e) is typically the most significant among these resistive elements. Consequently, R\u003csub\u003eCT\u003c/sub\u003e often refers specifically to \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCE\u0026ndash;electrolyte\u003c/sub\u003e unless otherwise specified. Among these resistances, the series resistance (R\u003csub\u003eS\u003c/sub\u003e) and the charge-transfer resistance at the counter electrode/electrolyte interface (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e) are critically dependent on the counter electrode properties [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Specially the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e value influences the number of electrons that get transferred from CE to the electrolyte to complete the DSSC circuit. To evaluate the catalytic behavior of the graphitic/AC and PEDOT: PSS incorporated CEs, the charge transfers resistances and sheet resistances of the symmetric cells were measured using EIS. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the Nyquist plot for both Pt and graphite/AC and PEDOT: PSSS/GR/AC symmetric cells. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e and sheet resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e) were determined through equivalent circuit fitting and calculated values are tabulated in Table \u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. As it can be seen from the table the series resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e) with PEDOT:PSS/GR/AC and GR/AC electrodes are 33.72 Ω and 50.08 Ω respectively. Both values are higher than the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e value of the Pt electrode (10.9 Ω ) This may be due to the lower conductivities of the carbon based electrodes. On the other hand, as it was observed by Murakami et al, this could be possibly due to the larger thickness and the rougher GR/AC film surfaces [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. A lower \u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e corresponds to a higher conductivity of the counter electrode and a better filling factor of the DSSC which is consistent with our FF values depicted in the Table \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e for the Pt CE [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Therefore, the DSSC with GR/AC CE showed lower values for the FF, \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e, and lower efficiency than the DSSCs with Pt CE [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The charge transfer resistance \u003cem\u003eR\u003c/em\u003e\u003csub\u003e1CT\u003c/sub\u003e or \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCE\u0026ndash;electrolyte\u003c/sub\u003e is an important parameter associated with charge transfer across the electrolyte/CE interface. As expected, the lowest \u003cem\u003eR\u003c/em\u003e\u003csub\u003e1CT\u003c/sub\u003e value of 6.55 Ω shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e corresponds to the Pt/electrolyte interface. The GR/AC/electrolyte interface shows much higher R\u003csub\u003e1CT\u003c/sub\u003e value of 118.4 Ω compared to the Pt/electrolyte interface. This is very likely caused by the higher resistivity of the nanoporous GR/AC composite compared to Pt. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003e1CT\u003c/sub\u003e value of PEDOT: PSS incorporated CE based DSSCs is 84.06 Ω and it is much lower than the DSSCs with GR/AC counter electrode but much higher than that of the DSSCs with Pt CE. Normally, a decreasing trend in \u003cem\u003eR\u003c/em\u003e\u003csub\u003e1CT\u003c/sub\u003e value is associated with an increasing trend in \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e for most of the DSSC systems studied as can be observed in this study too [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The higher efficiency in DSSCs with PEDOT: PSS composite mainly results from higher catalytic activity which is assigned to faster diffusion of redox couple in the electrolyte as observed by the Wu et al [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Incorporation of PEDOT: PSS in GR/AC counter electrode results in higher performance which mainly arises from the higher \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e. The enhanced \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e is mainly results from higher electro catalytic activity owing to lower \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e and diffusion resistance which is in line with the above morphological and electrochemical analysis [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSeries resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e) and the the charge transfer resistance \u003cem\u003eR\u003c/em\u003e\u003csub\u003e1CT\u003c/sub\u003e ( \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCE\u0026ndash;electrolyte\u003c/sub\u003e values of DSSCS with different CEs\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter Electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e1CT\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e50.08 \u0026plusmn; 0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e118.24 \u0026plusmn; 0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePEDOT:PSS/GR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e33.72 \u0026plusmn; 0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e84.06 \u0026plusmn; 0.31\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.60 \u0026plusmn; 0.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e9.11 \u0026plusmn; 0.23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eCyclic voltammetry (CV) analysis is an important and efficient tool for analyzing ion diffusivity and the catalytic mechanism acting in an electrochemical system [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The cyclic voltammetry analysis for electrodes was carried out by a three-electrode system. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows the cyclic voltamograms of Pt, Graphite /AC and PEDOT: PSS/GR/AC electrode, in which the potential ranged from \u0026minus;\u0026thinsp;0.2 to 1.2 V (vs. Ag/AgCl) at the scan rate of 50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Two pairs of redox peaks were observed in the cyclic voltammograms of all the CEs. The relative negative pair was assigned to the redox reaction as in Eq.\u0026nbsp;(1) and the positive one was assigned to the redox reaction in Eq.\u0026nbsp;(2) [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eI\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e + 2e \u0026minus; ⇌ 3I \u003csup\u003e\u0026minus;\u003c/sup\u003e ----------------(1)\u003c/p\u003e\n\u003ch3\u003e3I + 2e − → 2I ----------------(2)\u003c/h3\u003e\n\u003cp\u003eIn DSSCs, the reduction reaction of triiodide (I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) occurs at the counter electrode, which is crucial for completing the circuit and regenerating the dye molecules. Therefore, it is essential to study the redox behavior of the iodide/triiodide (I\u003csup\u003e\u0026minus;\u003c/sup\u003e/I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) couple at negative potentials [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. It has been reported that the electrocatalytic performance of a counter electrode for the reduction of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e in DSSCs is related to the cathodic peak current observed at more negative potentials. A higher cathodic peak current density indicates better catalytic activity of the counter electrode [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Apart from the as peak current density, counter electrode catalytic ability is estimated using peak to peak separation (ΔE\u003csub\u003epp\u003c/sub\u003e) of the oxidative and reduction peaks [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. The peak to peak separation is calculated from Eq.\u0026nbsp;(3). A higher cathodic peak current density indicates better catalytic activity of the counter electrode [\u003cspan additionalcitationids=\"CR42 CR43 CR44\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eΔ\u003cem\u003eE\u003c/em\u003e\u003csub\u003epp\u003c/sub\u003e = |\u003cem\u003eE\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e (anodic) \u0026ndash;\u003cem\u003eE\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e (cathodic)| -------------(3)\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the estimated electrochemical parameters including the |ΔE\u003csub\u003epp\u003c/sub\u003e | and the diffusion coefficient values of different counter electrodes obtained from CV measurements.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectrochemical parameters of different counter electrodes obtained from CV Measurements\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e|\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eOX1\u003c/sub\u003e|\u003c/p\u003e \u003cp\u003e(mA cm\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e|\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eRED1\u003c/sub\u003e|\u003c/p\u003e \u003cp\u003e( mA cm\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e|\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eOX1\u003c/sub\u003e|/ |\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eRED1\u003c/sub\u003e|\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e|\u003cem\u003eΔE\u003c/em\u003e\u003csub\u003epp\u003c/sub\u003e | (V)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eD\u003csub\u003en\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(x10\u003csup\u003e-4\u003c/sup\u003e)/cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePEDOT:PSS/GR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e14.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.89\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe reduction current peaks (cathodic peak) of the PEDOT: PSS/GR/AC electrode were much higher than that of the both Pt and the GR/AC electrodes. On the other hand, the reduction peak currents density of GR/AC based electrodes was also much greater than that of the Pt counter electrode. This could be attributed to the large active surface area of both the GR/AC and PEDOT: PSS/GR/AC electrodes. The higher the cathodic peak current density, better the catalytic activity of the counter electrode [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Moreover, the |\u003cem\u003eJ\u003c/em\u003e \u003csub\u003eOX1\u003c/sub\u003e| / |\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eRED1\u003c/sub\u003e| ratio is a parameter which is important in estimating the reversibility of the I\u003csup\u003e\u0026minus;\u003c/sup\u003e /I\u003csub\u003e3\u003c/sub\u003e \u003csup\u003e\u0026minus;\u003c/sup\u003e redox reaction [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The value of |\u003cem\u003eJ\u003c/em\u003e \u003csub\u003eOX1\u003c/sub\u003e| / |\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eRED1\u003c/sub\u003e| for the PEDOT: PSS/GR/AC is much closer to 1.00 than the corresponding values for the GR/AC CE, or even for the Pt cathode, suggesting that the reversible redox reaction I\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e is more stable on the PEDOT:PSS/GR/AC electrode than on the Pt electrode and the GR/AC electrode [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Based on the cyclic voltammetry results, the incorporation of PEDOT: PSS improves the catalytic activity of the composite CE. Similar behavior of these parameters was also observed by Wu et al in their studies on polyoxometalate-doped polypyrrole film electrodes [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] as well as by Duan et al with metal selenide alloy CEs in DSSCs [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. For a real DSSC device, a higher reversibility implies the rapid conversion of I\u003csub\u003e3\u003c/sub\u003e\u0026macr; into I \u0026macr; species for dye recovery. Therefore, more N719 molecules can excite electrons for electricity generation as observed with the highest \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eSC\u003c/sub\u003e in DSSCs fabricated with PEDOT: PSS/GR/AC counter electrode. The correlation among peak current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eRED1\u003c/sub\u003e), diffusion coefficient (\u003cem\u003eD\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e) and scan rate (ⱱ) can be expressed by the Randles-Sevcik Eq.\u0026nbsp;5.\u003c/p\u003e \u003cp\u003e \u003cem\u003eJ\u003c/em\u003e \u003csub\u003eRED1\u003c/sub\u003e = \u003cem\u003eKAC\u003c/em\u003e n\u003csup\u003e1.5\u003c/sup\u003e \u003cem\u003eD\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e \u003csup\u003e0.5\u003c/sup\u003e \u003cem\u003eⱱ\u003c/em\u003e \u003csup\u003e0.5 ----------------\u003c/sup\u003e (5)\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eK\u003c/em\u003e is a constant (=\u0026thinsp;2.69 x 10\u003csup\u003e5\u003c/sup\u003e) n is the number of electrodes contributing to charge transfer, \u003cem\u003eA\u003c/em\u003e is the electrode area and \u003cem\u003eC\u003c/em\u003e represents the bulk concentration of redox species [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Tafel polarization of all three counter electrodes were performed to further analyze the charge transfer kinetics at the interface of CE/electrolyte using a symmetric cell configuration. The polarization curves display the logarithmic current density as depicted in the Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the equilibrium state, the electron transfer rate can be determined from the intersection of the linear cathodic and anodic branches of the curves, which indicates the exchange current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eO\u003c/sub\u003e) [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. The \u003cem\u003eJ\u003c/em\u003e₀ is an essential indicator of the catalytic activity of the counter electrode. This is used to assess its effectiveness in reducing iodide ions. A higher \u003cem\u003eJ\u003c/em\u003e₀ value denotes greater catalytic activity of the counter electrode for iodide ion reduction [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. \u003cem\u003eJ\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e is inversely proportional to \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e with the following equation. \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eO\u003c/sub\u003e =\u003cem\u003eRT\u003c/em\u003e/\u003cem\u003enFR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e, where \u003cem\u003eR\u003c/em\u003e is the gas constant, \u003cem\u003eT\u003c/em\u003e is the absolute temperature, \u003cem\u003eF\u003c/em\u003e is the Faraday\u0026rsquo;s constant and \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCT\u003c/sub\u003e is the charge transfer resistance [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Furthermore, the limiting diffusion current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e), corresponding to the intersection of the cathodic branch with the Y-axis, is a parameter directly proportional to the diffusion coefficient (\u003cem\u003eD\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e) of the I⁻/I₃⁻ redox couple at the CE/electrolyte interface. This parameter can be used to estimate the diffusion performance of the redox couples. The highest \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e demonstrates the faster diffusion rate of the I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e reduction in the electrolyte. The trends of \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e would consistent with the Jo for all CEs. The exchange current density (\u003cem\u003eJ\u003c/em\u003e₀) can be calculated from the polarization region, while \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e can be measured from the diffusion region. The \u003cem\u003eD\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e value is directly proportional to diffusion coefficient (\u003cem\u003eD\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e) of the I\u003csup\u003e\u0026minus;\u003c/sup\u003e/ I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e redox couple at the CE/Electrolyte interface [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cem\u003eD\u003c/em\u003e \u003csub\u003en\u003c/sub\u003e = L (J\u003csub\u003eLim\u003c/sub\u003e) / 2nFC), where \u003cem\u003eD\u003c/em\u003e is the diffusion coefficient of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026macr;\u003c/sup\u003e, l is the thickness of diffusion layer, \u003cem\u003eC\u003c/em\u003e is the concentration of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026macr;\u003c/sup\u003e [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. Estimated \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eO\u003c/sub\u003e values and \u003cem\u003eJ\u003c/em\u003e \u003csub\u003eLIM\u003c/sub\u003e values are tabulated in the Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 7\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eElectrochemical parameters of different electrodes extracted from EIS measurements and Tafel plot measurements.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCounter electrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003elog \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eO\u003c/sub\u003e ( mA cm\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003elog \u003cem\u003eJ\u003c/em\u003e lim ( mA cm\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePEDOT:PSS/GR/AC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.73\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe \u003cem\u003eJ\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e value of the cells with GR/AC, PEDOT:PSS/GR/AC and Pt electrode are approximately 0.85 mA cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e and 1.04 mA cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e and 1.84 mA cm\u003csup\u003e\u0026minus;2\u003c/sup\u003e respectively. This indicates that the PEDOT: PSS/GR/AC CEs in the DSSCs can handle the back reaction more efficiently than the GR/AC counter electrode, and contribute toward improving the current in the device as observed in the \u003cem\u003eJ\u003c/em\u003e\u003csub\u003esc\u003c/sub\u003e values depicted in the Table \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. However, the low values of \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eO\u003c/sub\u003e than the Pt CE indicates the lower conductivity in comparison with that of the Pt CEs. Figure\u0026nbsp;12 and Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e follows the same order as \u003cem\u003eJ\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e. In summary, according to the systematic evaluation of electrocatalytic activity for the PEDOT: PSS/GR/AC counter electrode, it is as effective and sufficient as Pt to catalyze the reduction reaction of triiodide to iodide. Similar results for the \u003cem\u003eJ\u003c/em\u003eo and \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e values of the Pt electrodes were observed by several authors like Wei et al [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] and Yue et al [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e follows the same order as \u003cem\u003eJ\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e. As shown in the Table \u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the \u003cem\u003eJ\u003c/em\u003e\u003csub\u003elim\u003c/sub\u003e values lie in the order of Pt\u0026thinsp;\u0026gt;\u0026thinsp;PEDOT:PSS/GR/AC\u0026thinsp;\u0026gt;\u0026thinsp;GR/AC, indicating that PEDOT:PSS/GR/AC can effectively catalyze the reduction of I\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and reduce the concentration near the electrode surface due to its high catalytic ability, thereby accelerating the diffusion rate of redox to the electrode surface [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Therefore, the photovoltaic performance of the DSSCs, in agreement with results obtained in CV, EIS and Tafel measurements. Hence, from this study one can conclude that PEDOT: PSS/GR/AC composite CE has a great ability to trigger the reduction of triiodide ions at the electrolyte/CE interface though it cannot outperform the Pt CE. In summary, according to the systematic evaluation and study of electrocatalytic activity for the PEDOT: PSS/GR/AC counter electrode, it is as effective and sufficient as Pt to catalyze the reduction reaction of triiodide to iodide.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eIn this study, we developed a novel three-component composite carbon counter electrode (tri-carbon) utilizing Sri Lankan vain graphite, activated carbon and PEDOT: PSS, which can be used to improve the electrochemical performance of graphite. The integration of activated carbon and PEDOT into the graphite matrix reduced charge transfer resistance, leading to an increase in JSC and consequently improved electrocatalytic activity and charge transport, as evidenced by EIS and Tafel measurements. The tri-carbon counter electrode demonstrated superior charge transfer properties and catalytic ability due to the synergistic effects of charge transfer kinetics, catalytic properties of I\u003csub\u003e3\u003c/sub\u003e\u0026macr;, and electrical conductivity. DSSCs assembled with the tri-carbon counter electrode, GR/AC, and Pt counter electrode with Ru N719 dye-sensitized photoanodes achieved efficiencies of 4.60%, 4.0%, and 6.05% respectively. Our results indicate that the composite materials incorporating PEDOT have significant potential for DSSC applications and warrant further investigation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eG.K.R. Senadeera and P. Ekanayake were responsible for funding acquisition, resources, conceptualization, and writing the original draft. Formal analysis, investigation, data curation, and visualization were carried out by R.M.S.S. Rasnayake, J.M.K.W. Kumari, P.U. Sandunika, D.L.N. Jayathilaka, and T. Jaseetharan. Methodology, validation, project administration, and supervision were managed by G.K.R. Senadeera, M.A.K.L. Dissanayaka, and P. Ekanayake. All authors contributed to validation, reviewed the manuscript, and agreed to its publication.\u003c/p\u003e\u003ch2\u003e6. Acknowledgment\u003c/h2\u003e \u003cp\u003eThe authors gratefully acknowledge the Open University of Sri Lanka, National Institute of Fundamental Studies, Sri Lanka and the Universiti Brunei Darussalam for providing necessary financial assistance and the infrastructure facility.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGr\u0026auml;tzel M (2003) Dye-sensitized solar cells. 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Energy 188, 603\u0026ndash;608. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.solener.2019.06.034\u003c/span\u003e\u003cspan address=\"10.1016/j.solener.2019.06.034\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYue, G., Li, F., Tan, F., Li, G., Chena, C and Wub, J., (2014) Nickel sulfide films with significantly enhanced electrochemical performance induced by self-assembly of 4-aminothiophenol and their application in dye-sensitized solar cells, RSC Adv., 2014, 4, 64068, DOI: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/c4ra10978c\u003c/span\u003e\u003cspan address=\"10.1039/c4ra10978c\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Graphite, activated carbon, PEDOT:PSS counter electrode, dye-sensitized solar cell","lastPublishedDoi":"10.21203/rs.3.rs-4594353/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4594353/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDeveloping an efficient material as a counter electrode (CE) with excellent catalytic activity, intrinsic stability, and low cost is essential for the commercial application of dye-sensitized solar cells (DSSCs). Photovoltaic properties DSSCs fabricated with low-cost and platinum-free CEs based on different mixtures of carbon allotropes graphite (GR), activated carbon (AC) and PEDOT: PSS films. The DSSCs assembled with PEDOT: PSS/GR/AC showed an impressive photovoltaic conversion efficiency of 4.60%, compared to 4.06% for DSSCs with GR/AC CE or 1.66% for PEDOT: PSS alone or 6.56 % for Pt under the illumination 100 mW cm\u003csup\u003e− 2\u003c/sup\u003e (AM 1.5 G) due to the superior electrocatalytic activity and the conductivity of AC and PEDOT: PSS. \u0026nbsp;The fabricated carbon counter electrodes were extensively characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, cyclic voltammetry (CV), Tafel measurements and electrochemical impedance spectroscopy (EIS). The CV, EIS and Tafel measurements indicated that the PEDOT: PSS/Graphite/AC composite film has low charge-transfer resistance on the electrolyte/CE interface and high catalytic activity for the reduction of triiodide to iodide than the GR/AC CEs.\u0026nbsp; It is potentially feasible that such a carbon configuration can be used as a counter electrode, replacing the more expensive Pt in DSSCs.\u003c/p\u003e","manuscriptTitle":"Novel Platinum-Free Counter-Electrode with PEDOT: PSS-Treated Graphite/Activated Carbon for Efficient Dye-Sensitized Solar Cells","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-18 16:04:57","doi":"10.21203/rs.3.rs-4594353/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-28T11:07:15+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-25T13:01:34+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-07-19T02:47:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"224517325542776417400085630136057175150","date":"2024-07-11T09:33:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"121251838858091455114031248924241392797","date":"2024-07-10T20:31:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-27T03:51:43+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-26T01:50:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"327235933266442960608808581843018350457","date":"2024-06-24T15:33:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"167191886810685609295017730382824055907","date":"2024-06-24T09:57:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8261927762353433417862042063397420013","date":"2024-06-21T01:17:39+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-20T11:56:56+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-06-20T00:50:31+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-06-20T00:50:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2024-06-17T13:11:51+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"da67e4df-dacd-4dab-b597-7481e2d0323d","owner":[],"postedDate":"July 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-10-04T21:53:16+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-18 16:04:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4594353","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4594353","identity":"rs-4594353","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}