A novel hierarchical Pt- and FTO-free counter electrode for dye-sensitized solar cell

A novel hierarchical Pt- and FTO-free counter electrode (CE) for the dye-sensitized solar cell (DSSC) was prepared by spin coating the mixture of TiO₂ nanoparticles and poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) solution onto the glass substrate. Compared with traditional Pt/FTO CE, the cost of the new CE is dramatically reduced by the application of bilayer TiO₂-PEDOT:PSS/PEDOT:PSS film and the glass substrate. The sheet resistance of this composite film is 35 Ω sq⁻¹ and is low enough to be used as an electrode. The surface morphologies of TiO₂-PEDOT:PSS layer and modified PEDOT:PSS layer were characterized by scanning electron microscope, which shows that the former had larger surface areas than the latter. Electrochemical impedance spectra and Tafel polarization curves prove that the catalytic activity of TiO₂-PEDOT:PSS/PEDOT:PSS/glass CE is higher than that of PEDOT:PSS/FTO CE and is similar to Pt/FTO CE''s. This new fabricated device with TiO₂-PEDOT:PSS/PEDOT:PSS/glass CE achieves a high power conversion efficiency (PCE) of 4.67%, reaching 91.39% of DSSC with Pt/FTO CE (5.11%).     

Low temperature preparation of a high performance Pt/SWCNT counter electrode for flexible dye-sensitized solar cells

A platinum/single-wall carbon nanotube (Pt/SWCNT) film was sprayed onto a flexible indium-doped tin oxide coated polyethylene naphthalate (ITO/PEN) substrate to form a counter electrode for use in a flexible dye-sensitized solar cell using a vacuum thermal decomposition method at low temperature (120 °C). The obtained Pt/SWCNT electrode showed good chemical stability and light transmittance and had lower charge transfer resistance and higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction compared to the flexible Pt electrode or a commercial Pt/Ti electrode. The light-to-electric energy conversion efficiency of the flexible DSSC based on the Pt/SWCNT/ITO/PEN counter electrode and the TiO₂/Ti photoanode reached 5.96% under irradiation with a simulated solar light intensity of 100 mW cm⁻². The efficiency was increased by 25.74% compared to the flexible DSSC with an unmodified Pt counter electrode.     

A novel high-performance counter electrode for dye-sensitized solar cells

A novel Pt counter electrode for dye-sensitized solar cells (DSC) was prepared by thermal decomposition of H₂PtCl₆ on NiP-plated glass substrate. The charge-transfer kinetic properties of the platinized NiP-plated glass electrode (Pt/NiP electrode) for triiodide reduction were studied by electrochemical impedance spectroscopy. Pt/NiP electrode has the advantage over the platinized FTO conducting glass electrode (Pt/FTO electrode) in increasing the light reflectance and reducing the sheet resistance leading to improve the light harvest efficiency and the fill factor of the dye-sensitized solar cells effectively. The photon-to-current efficiency and the overall conversion efficiency of DSC using Pt/NiP counter electrode is increased by 20% and 33%, respectively, compared to that of using Pt/FTO counter electrode. Examination of the anodic dissolution and the long-term test on the variation of charge-transfer resistance indicates the good stability of the Pt/NiP electrode in the electrolyte containing iodide/triiodide.     

Stability study of carbon-based counter electrodes in dye-sensitized solar cells

This study describes a systematic investigation of the stability of a carbon/TiO₂ counter electrode for use in dye-sensitized solar cells (DSSCs). In this system, nanoparticle additives were introduced by adding Ti-hydrogel. The additives then bound carbon particles and enhanced the adhesion of carbon materials to the conductive substrate. After introducing the Ti-hydrogel into the carbon paste, the carbon/Ti-hydrogel composited counter electrode (HC-CE) showed a better conductivity and stability compared with that of the carbon counter electrode (C-CE), while the catalytic activity was not influenced. The device based on the HC-CE showed superior power conversion efficiency (6.3%) and long-term stability over the device based on the C-CE (5.8%).     

A study of TiO2/carbon black composition as counter electrode materials for dye-sensitized solar cells

This study describes a systematic approach of TiO₂/carbon black nanoparticles with respect to the loading amount in order to optimize the catalytic ability of triiodide reduction for dye-sensitized solar cells. In particular, the cell using an optimized TiO₂ and carbon black electrode presents an energy conversion efficiency of 7.4% with a 5:1 ratio of a 40-nm TiO₂ to carbon black. Based on the electrochemical analysis, the charge-transfer resistance of the carbon counter electrode changed based on the carbon black powder content. Electrochemical impedance spectroscopy and cyclic voltammetry study show lower resistance compared to the Pt counter electrode. The obtained nanostructures and photo electrochemical study were characterized.     

Wurtzite copper-zinc-tin sulfide as a superior counter electrode material for dye-sensitized solar cells

Wurtzite and kesterite Cu₂ZnSnS₄ (CZTS) nanocrystals were employed as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Compared to kesterite CZTS, the wurtzite CZTS exhibited higher electrocatalytic activity for catalyzing reduction of iodide electrolyte and better conductivity. Accordingly, the DSSC with wurtzite CZTS CE generated higher power conversion efficiency (6.89%) than that of Pt (6.23%) and kesterite CZTS (4.89%) CEs.     

Effect of TiO2 nanotubes with TiCl4 treatment on the photoelectrode of dye-sensitized solar cells

In this study, we used the electrochemical anodization to prepare TiO₂ nanotube arrays and applied them on the photoelectrode of dye-sensitized solar cells. In the field emission scanning electron microscopy analysis, the lengths of TiO₂ nanotube arrays prepared by electrochemical anodization can be obtained with approximately 10 to 30 μm. After titanium tetrachloride (TiCl₄) treatment, the walls of TiO₂ nanotubes were coated with TiO₂ nanoparticles. XRD patterns showed that the oxygen-annealed TiO₂ nanotubes have a better anatase phase. The conversion efficiency with different lengths of TiO₂ nanotube photoelectrodes is 3.21%, 4.35%, and 4.34% with 10, 20, and 30 μm, respectively. After TiCl₄ treatment, the efficiency of TiO₂ nanotube photoelectrode for dye-sensitized solar cell can be improved up to 6.58%. In the analysis of electrochemical impedance spectroscopy, the value of R_k (charge transfer resistance related to recombination of electrons) decreases from 26.1 to 17.4 Ω when TiO₂ nanotubes were treated with TiCl₄. These results indicate that TiO₂ nanotubes treated with TiCl₄ can increase the surface area of TiO₂ nanotubes, resulting in the increase of dye adsorption and have great help for the increase of the conversion efficiency of DSSCs.     

TiO2 micro-flowers composed of nanotubes and their application to dye-sensitized solar cells

TiO₂ micro-flowers were made to bloom on Ti foil by the anodic oxidation of Ti-protruding dots with a cylindrical shape. Arrays of the Ti-protruding dots were prepared by photolithography, which consisted of coating the photoresists, attaching a patterned mask, illuminating with UV light, etching the Ti surface by reactive ion etching (RIE), and stripping the photoresist on the Ti foil. The procedure for the blooming of the TiO₂ micro-flowers was analyzed by field emission scanning electron microscopy (FESEM) as the anodizing time was increased. Photoelectrodes of dye-sensitized solar cells (DSCs) were fabricated using TiO₂ micro-flowers. Bare TiO₂ nanotube arrays were used for reference samples. The short-circuit current (J_sc) and the power conversion efficiency of the DSCs based on the TiO₂ micro-flowers were 4.340 mA/cm² and 1.517%, respectively. These values of DSCs based on TiO₂ micro-flowers were higher than those of bare samples. The TiO₂ micro-flowers had a larger surface area for dye adsorption compared to bare TiO₂ nanotube arrays, resulting in improved J_sc characteristics. The structure of the TiO₂ micro-flowers allowed it to adsorb dyes very effectively, also demonstrating the potential to achieve higher power conversion efficiency levels for DSCs compared to a bare TiO₂ nanotube array structure and the conventional TiO₂ nanoparticle structure.     

Electrophoretic deposition of carbon nanotubes films as counter electrodes of dye-sensitized solar cells

Carbon nanotubes (CNTs) films have been successfully fabricated by electrophoretic deposition (EPD) technique and used as counter electrodes of dye-sensitized solar cells (DSSCs). The CNTs counter electrodes consisting of a large number of bamboo-like structures with defect-rich edge planes exhibit a highly interconnected network structure with high electrical conductivity and good catalytic activity. A high photovoltaic conversion efficiency of 7.03% is achieved for DSSCs based on the CNTs counter electrodes, which is comparable to the cell based on conventional Pt counter electrode at one sun (AM 1.5G, 100 mW cm⁻²). The results suggest that the present synthetic strategy provides a potential feasibility for the fabrication of low-cost flexible counter electrodes of DSSCs using a facile deposition technique from an environmentally “friendly” solution at low temperature.     

Micro–meso hierarchical porous carbon as low-cost counter electrode for dye-sensitized solar cells

A micro–meso hierarchical porous carbon with low crystallinity was prepared by a combination of self-assembly and post activation and explored as a counter electrode in dye-sensitized solar cells. Pore structure analysis showed that the pristine mesopores were basically preserved during activation and the micropores were mainly generated within the mesopore wall. Due to its low crystallinity and unique pore-structure including both mesopores and micropores, hierarchical porous carbon exhibited a relatively higher electrocatalytic activity for triiodide reduction, as compared with the pristine mesoporous carbon electrode. This enhanced electrocatalytic activity is beneficial for improving the photovoltaic performance of dye-sensitized solar cells. Under irradiation of 100 mW cm⁻², the dye-sensitized solar cell with hierarchical porous carbon counter electrode showed an overall conversion efficiency of 6.48%, which was 11.5% higher than that of the cell with pristine mesoporous carbon counter electrode.     

Electropolymerization of a poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes counter electrode for dye-sensitized solar cells and characterization of its performance

Composite films of poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes (PEDOT–MWCNT) were fabricated by a simple oxidative electropolymerization method. These films were formed on fluorine-doped, tin oxide, glass substrates as counter electrodes (CEs) of platinum-free, dye-sensitized solar cells (DSSCs). The surface morphology, formation mechanism and electrochemical nature of PEDOT–MWCNT films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The SEM and AFM images showed that PEDOT–MWCNT films were more porous than PEDOT films. CV and AC impedance spectroscopy revealed that the PEDOT–MWCNT electrode had higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction and a smaller charge transfer resistance than the PEDOT electrodes. The energy conversion efficiency of the DSSC with a PEDOT–MWCNT CE was 13.0% higher than with a PEDOT CE using the same conditions with a ruthenium sensitizer.     

Improvement of performance of dye-sensitized solar cells based on electrodeposited-platinum counter electrode

Platinum nanoparticle was electrodeposited on FTO conducting glass substrate as counter electrode for application in dye-sensitized solar cells (DSSCs). Images of transmission electron microscope (TEM) and Scanning Electron Microscope (SEM) showed that platinum nanoparticle was with the mean size of 20-30 nm and was homogeneously distributed on the surface of the FTO conductive glass sheet. Using such a counter electrode, DSSC showed a 6.40% overall energy conversion efficiency under one sun illumination. It exhibited the same high-performance as the DSSC with a platinum counter electrode prepared by electroplating. Furthermore, the present preparation method for the platinum counter electrode has the advantage of low platinum loading and transparence.     

A natural tomato slurry as a photosensitizer for dye-sensitized solar cells with TiO2/CuO composite thin films

We have studied the performance of dye-sensitized solar cells by employing natural dye “anthocyanins” extracted from the tomato slurry as a sensitizer for the TiO₂/CuO photoanode. The extracts were anchored on TiO₂/CuO films deposited on an ITO substrate which was used as a photoanode. The dye adsorbed TiO₂/CuO films electrode, the copper plate as a counter electrode, and iodolyte as an electrolyte were assembled into DSSCs. The conversion efficiency of the DSSCs was found to be 2.96% with a V_OC of 0.615 V, J_SC of 6.6 mA/cm², and an FF of 0.73. This work highlights the use of contribution of the tomato slurry as a natural sensitizer to enhance the efficiency of DSSCs.     

Conversion enhancement of flexible dye-sensitized solar cells based on TiO2 nanotube arrays with TiO2 nanoparticles by electrophoretic deposition

We prepared highly ordered titanium dioxide nanotube arrays (TNAs) by anodizing Ti foils in F⁻ containing electrolyte. The thickness and dye loading amount of TNAs were 26 μm and 1.06 × 10⁻⁷ mol cm⁻², respectively. TiO₂ nanoparticles (TNPs) were electrophoretically deposited on the inner wall of nanotube to produce coated nanotube arrays (TNAP). The dye loading was increased to 1.56 × 10⁻⁷ mol cm⁻², and the electron transport rate improved. TNAs and TNAP were sensitized with ruthenium dye N3 to yield dye-sensitized TiO₂ nanotube solar cells. The power conversion efficiency of TNA-based dye-sensitized solar cells (DSSCs) was 4.28%, whereas the efficiency of TNAP-based DSSCs increased to 6.28% when illuminated from the counter electrode. The increase of power conversion efficiency of TNAP-based DSSCs is ascribed to the increased surface area of TNAs and the faster electron transport rate.     

High-performance and low platinum loading electrodeposited-Pt counter electrodes for dye-sensitized solar cells

This study demonstrates platinum (Pt) counter electrodes with low charge-transfer resistance (R_ct), low Pt loading and high active surface area can be obtained within 30 s by using the direct-current deposition in the presence of 3-(2-aminoethylamino)propyl-methyldimethoxysilane (Me-EDA-Si) as an additive. The addition of appropriate Me-EDA-Si can not only enhance the current efficiency but also inhibit the growth of semicircle-like grains, thus resulting in Pt electrode with high active surface area. Consequently, the dye-sensitized solar cells (DSSCs) fabricated with so-prepared Pt electrodes exhibited cell efficiency of 7.39% while 0.01 vol% Me-EDA-Si was added, which is much superior to that with sputtered-Pt electrodes under the same assembly conditions.     

Effect of TiO2 rutile nanorods on the photoelectrodes of dye-sensitized solar cells

In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO₂ nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO₂ thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells.     

3-D solar cells by electrochemical-deposited Se layer as extremely-thin absorber and hole conducting layer on nanocrystalline TiO2 electrode

Ag₂S quantum dots were deposited on the surface of TiO₂ nanorod arrays by a two-step photodeposition. The prepared TiO₂ nanorod arrays as well as the Ag₂S deposited electrodes were characterized by X-ray diffraction, scanning electron microscope, and transmission electron microscope, suggesting a large coverage of Ag₂S quantum dots on the ordered TiO₂ nanorod arrays. UV–vis absorption spectra of Ag₂S deposited electrodes show a broad absorption range of the visible light. The quantum dot-sensitized solar cells (QDSSCs) based on these electrodes were fabricated, and the photoelectrochemical properties were examined. A high photocurrent density of 10.25 mA/cm² with a conversion efficiency of 0.98% at AM 1.5 solar light of 100 mW/cm² was obtained with an optimal photodeposition time. The performance of the QDSSC at different incident light intensities was also investigated. The results display a better performance at a lower incident light level with a conversion efficiency of 1.25% at 47 mW/cm².     

Nanocomposites of Bi5FeTi3O15 with MoS2 as novel Pt-free counter electrode in dye-sensitized solar cells

Bi₅FeTi₃O₁₅ (BFTO) nanofibers with diameters in the range of 40–100 nm have been fabricated by sol-gel based electrospinning technique. The structure and morphology of the nanofibers were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The MoS₂ nanoparticles are uniformly dispersed into the BFTO, forming nanocomposites. The optical bandgap of the nanocomposites decreases as MoS₂ content increases. The nanocomposites with different MoS₂ contents serve as low-cost counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Through photocurrent–voltage curves, electrochemical impedance spectroscopy and Tafel curves, the performance of the CEs indicates that the charge transfer resistance on the electrolyte-electrode interface lower and the catalytic activity for reduction of triiodide to iodide enhance with the increase of MoS₂ concentration. The DSSC with the CE exhibits a power conversion efficiency of 5.20% after the optimization of the content of MoS₂, which is almost 24 times larger than that of the pure BFTO CE.     

Enhancing the performance of dye-sensitized solar cells based on an organic dye by incorporating TiO2 nanotube in a TiO2 nanoparticle film

The photoelectrochemical properties of a high molar extinction coefficient charge transfer organic dye containing thienylfluorene segment called FL, and the effect of incorporating TiO₂ nanotube (TiNT) in TiO₂ nanoparticle film along with the above dye on the photovoltaic performance of dye-sensitized solar cells (DSSCs) were investigated. The influence of soaking time of the TiO₂ electrode in dye solution and the effect of varying its concentration, on the solar cell efficiency was also studied. Cyclic voltammetric (CV) analysis revealed the linear relationship between the anodic peak current and the scan rate, indicating a surface-confined diffusion process.The surface morphology of TiNT was characterized using SEM, TEM and XRD. The open-circuit voltage (V_OC) of the DSSC increased with the increase in the wt% of TiNT and shows optimal value at about 5 wt%, which is correlated with the suppression of the electron recombination as found out from the electron lifetime studies.The electrochemical impedance spectroscopy (EIS) technique was employed to quantify the charge transport resistance (R_ct) and electron lifetime under different ratios of the TiNT/nanoparticle. The electron lifetimes of the DSSCs based on FL and N3 dye were very close to one another and the DSSC based on the FL showed respectable photovoltaic performance of ca. 7.8% under the light intensity of 100 mW cm⁻² (AM 1.5G).     

A composite poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) and Pt film as a counter electrode catalyst in dye-sensitized solar cells

A composite poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]-dioxepine) and platinum (PProDOT-Et₂/Pt) film was prepared for using as a counter electrode (CE) catalyst in a dye-sensitized solar cell (DSSC). Four composite films were prepared by electropolymerization of ProDOT-Et₂ on indium tin oxide (ITO) conducting glass, followed by Pt sputtering for 10, 30, 120, and 720 s. The Pt content in the composite film was verified by energy dispersive X-ray spectroscopy (EDX). The composite films possessed three-dimensional (3D) porous structures, as determined by scanning electron microscopy (SEM). The DSSC with the composite film that was subject to 10 s of Pt deposition (PProDOT-Et₂/Pt-10 s) exhibited the highest solar to electricity conversion efficiency (η) of 6.68%, while the cells with the bare polymer film (PProDOT-Et₂) and Pt that was sputtered for 720 s (s-Pt-720 s) demonstrated efficiencies of 4.76% and 6.43%, respectively. The cell photovoltaic parameters were substantiated through dark current, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analyses. Incident photon-to-current conversion efficiency (IPCE) curves were used to explain the cell photocurrent behaviors.