Facile synthesis of tungsten carbide nanorods and its application as counter electrode in dye sensitized solar cells

Tungsten carbide nanorods (WC-NRs) are synthesized by pseudomorphic transformation of chemically synthesized W₃O₈ nanorods using a high-temperature method. The WC-NRs was introduced into dye sensitized solar cell (DSSC) as counter electrode (CE) catalyst to replace the expensive platinum (Pt). The synthesized WC-NRs were characterized by field emission scanning electron microscopy (FESEM), BET surface area analysis and powder X-ray diffraction (PXRD) measurements. The electrochemical properties of WC-NRs counter electrode were studied using electrochemical impedance spectroscopy (EIS) techniques. The photovoltaic performance of the DSSC with WC-NRs counter electrode was evaluated under simulated standard global AM 1.5G sunlight (100 mW/cm²). The solar to electrical energy conversion efficiency (η) of the WC-NRs with binder and binder free based DSSC was found to be 1.92% and 0.59% respectively. The cell performance can be attributed to the WC-NRs network, catalytic redox activity and 1-D efficient charge-transfer network. Such WC-NRs configuration as CE provides a potential feasibility for counter electrodes in DSSC applications.     

Polypyrrole-coated cotton fabrics prepared by electrochemical polymerization as textile counter electrode for dye-sensitized solar cells

Textile-based wearable electronics provides the combined advantages of both electronics and textiles, such as flexibility, stretchability and lightweight. Much effort has been dedicated to achieve flexible photovoltaic power for wearable electronics. Here, we have demonstrated polypyrrole (PPy) coated cotton fabrics as textile counter electrode (CE) in dye-sensitized solar cells (DSSCs). PPy is deposited on the Ni-coated cotton fabrics as catalytic material by electrochemical polymerization of pyrrole. The highly conductive PPy-coated fabric electrode with a surface resistance of 5.0 Ω sq⁻¹ shows reasonable catalytic activity for the reduction of triiodide ion. The DSSC fabricated with the PPy-coated fabric CE exhibits a power conversion efficiency as high as ∼3.83% under AM 1.5 illumination.     

Studies of high-efficient and low-cost dye-sensitized solar cells

Dye-sensitized solar cell (DSSC) is a new type of photoelectric device. To commercialize DSSC successfully, it is necessary to further improve the efficiency of energy conversion and reduce its cost. Nitrogen-doped (N-doped) TiO2 photoanode, the carbon counter electrode (CE), and a new type of hybrid photoanode were investigated in this study. The conversion efficiency of the DSSC reached by 10.10% as the DSSC was fabricated with the N-doped photoanode, and this efficiency is much higher than that of the undoped-DSSC with 8.90%; as the low-cost carbon was used as CE, the efficiency of the DSSC was 7.50%, it was as samilar as that of Pt CE (7.47%); the hybrid DSSC with multilayer photoanode by the film-transfer technique achieved a panchromatic response and a superposed short circuit current density (Jsc) by using two complementary dyes.     

Graphene nanosheets as counter electrode with phenoxazine dye for efficient dye sensitized solar cell

Efficient dye sensitized solar cells (DSSCs) are developed using phenoxazine (POZ) based organic dye (WS5) and graphene nanosheets (GNs) counter electrode (CE). Being organic, both these materials are used together to explore compatibility of organic materials in current DSSCs. Organic dye with POZ moiety is synthesized and graphene oxide nanosheets (GONs) are spin coated on FTO glass and thermally reduced afterwards. To increase the performance of WS5 through decreased dye aggregation, deoxycholic acid (DCA) is added to it. The results of adding DCA are observed and compared using UV–Vis spectroscopy, external quantum efficiency (EQE), electrochemical impedance spectroscopy (EIS) and photovoltaic conversion efficiency (PCE). Prepared organic dye based DSSC cell results in a high PCE of 6.61%. The optimized WS5 dye and GNs CE, shows PCE of 5.77% and the GNs CE compared to Pt CE results in almost identical charge transfer resistance value at the CE/electrolyte interface. Low cost of this designed organic dye and GNs and the PCE results indicate that this combination may result in the reduction of cost of current DSSCs and the realization that expensive and rare inorganic materials can be replaced with organic ones in future.     

Durability test of PVP‐capped Pt nanoclusters counter electrode for highly efficiency dye‐sensitized solar cell

In this paper, the durability of PVP‐capped Pt nanoclusters counter electrode (PVP‐Pt CE) for dye‐sensitized solar cell (DSSC) has been extensively evaluated including electrochemical reaction durability, thermal stress durability and light soaking durability. It is revealed that PVP‐Pt CE exhibits both electrochemical and thermal durability by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) test. Moreover, DSSC containing PVP‐Pt CE shows over 9.37% conversion efficiency in highly volatile electrolyte system. As to device thermal durability, both low‐volatile and non‐volatile electrolyte systems were tested and the results show relative efficiency can maintain more than 85% after accelerated thermal test at 85°C for 1000 h, and 110% after 60°C for 1000 h. Finally, after continuous light soaking test under 60°C for 1000 h, the relative efficiency can still maintain at 94%. Copyright © 2011 John Wiley & Sons, Ltd.     

High performance platinum nanofibers with interconnecting structure using in dye-sensitized solar cells

Platinum nanofibers (PtNFs) with interconnecting structure are prepared by a simple electrospun method and novel film forming technique, which are used as the counter electrode (CE) materials for the dye-sensitized solar cells (DSSCs). Electron microscope images demonstrate that PtNFs are constituted by Pt nanoparticles. Cyclic voltammetry measurements indicate that PtNF CE has an excellent catalytic activity for the reduction of triiodide to iodide. DSSC based on PtNF CE achieves an enhanced photovoltaic conversion efficiency of 9.31% compared to that of DSSC based on Pt CE (7.32%) prepared by the thermal decomposition, owing to the three-dimensional interconnecting nanostructure has abundant catalytic surfaces, large contact area with the electrolyte, and lots of electronic transmission channels. DSSC efficiency based on PtNF CE remains 90.08% after continuous scanning 1000 s under an open system without any sealing in ambient atmosphere, and 83.19% of the efficiency is remained after 1000 h under a strictly packaging for the device application.     

A transparent honeycomb-like poly(3,4-ethylenedioxythiophene)/multi-wall carbon nanotube counter electrode for bifacial dye-sensitized solar cells

A novel transparent honeycomb-like poly(3,4-ethylenedioxythiophene)/multi-wall carbon nanotube (PEDOT/MWCNT) electrode served as a counter electrode (CE) for the bifacial dye-sensitized solar cell (DSSC) has been fabricated on the fluorine-doped tin oxide (FTO) glass using a sacrificial template of poly(methyl methacrylate) for the first time. Cyclic voltammetry and electrochemical impedance spectroscopy measurements indicate that the honeycomb-like PEDOT/MWCNT CE has a higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction and a smaller charge transfer resistance than those of the flat PEDOT CE. Ultraviolet–visible spectrophotometer measurement indicates that the PEDOT/MWCNT CE with honeycomb-like nanostructure demonstrates high transparency for the backside illumination. The bifacial DSSC based on this honeycomb-like PEDOT/MWCNT CE shows conversion efficiencies of 9.07% and 5.62% from front and rear side illumination, respectively, which are higher than those of the bifacial DSSC based on the flat PEDOT CE (7.51% and 3.49% respectively).     

A nanostructure-based counter electrode for dye-sensitized solar cells by assembly of silver nanoparticles

A nanostructure-based Pt counter electrode for dye-sensitized solar cells (DSSCs) is fabricated by assembly of silver nanoparticles on glass substrate and deposition of a thin Pt layer. This typical counter electrode has several unique behaviors such as good conductivity, quasi-uniform undulating morphology and high surface area. Studies indicate that the application of the FTO-free nanostructure-based Pt counter electrode in DSSCs can decrease the charge-transfer resistance of the Pt/electrolyte interface, enlarge the light pathway and enhance the light reabsorption superior to the devices with planar Pt counter electrode. In addition, theoretical analysis and experimental study demonstrate that the hot electrons injection effect caused by Localized Surface Plasmon Resonance effect of silver nanoparticles enhances the charge transport characteristic at the Pt/electrolyte interface, and this SPR effect makes the certain contributions on the enhancement of the photovoltaic performance of DSSCs. Compared to the DSSC with traditional planar counter electrode, the incident photon-to-current conversion efficiency, short-circuit current, and power conversion efficiency of DSSCs with nanoparticulate structure are increased by 1.117 times, 1.156 times, and 1.145 times, respectively; and the final power conversion efficiency (PCE) increases from 6.95% to 7.96%.     

Investigation of graphene nanosheets as counter electrodes for efficient dye-sensitized solar cells

In this study, graphene nanosheets (GNs) were used to fabricate novel counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The electrode properties of various CEs were comprehensively analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectrometry (EDS), and cyclic voltammetry (CV). DSSCs with various GN CEs were characterized using current density–voltage (J–V), incident photo-to-current conversion efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) measurements. The results show that GN CEs sintered at 400 °C in a nitrogen atmosphere for 30 min yielded the optimal electrode properties and DSSC efficiency. This study also fabricated GN–Pt composite and GN–Pt stacked CEs for the DSSCs, and the influences of the CEs on the efficiency of the DSSCs were investigated. The results show that the GN–Pt stacked CEs yielded the optimal electrochemical catalytic properties and DSSC efficiency. The power conversion efficiency of the DSSCs based on GN–Pt stacked CEs yielded a 16.7% improvement compared with conventional Pt CEs.     

Nanoporous platinum counter electrodes by glancing angle deposition for dye-sensitized solar cells

We report an effective way to produce nanoporous Pt counter electrodes of dye-sensitized solar cells by the glancing-angle deposition (GLAD) technique. By controlling the orientation of the substrate relative to the incident Pt vapor flux during the deposition, nanoporous films composed of inclined nm-scale columns were produced through the self-shadowing effect. Pt counter electrodes having varied nanoporous structures were characterized for their morphological and electrochemical properties, and were subjected to device studies to establish the correlation with DSSC characteristics/performances. The results suggest that the nanoporous GLAD Pt electrodes can effectively enhance active surface areas, the catalytic ability and charge exchange at the Pt/electrolyte interface of a DSSC. As a result, the quantum efficiency, short-circuit current, and power conversion efficiency of the DSSC can be enhanced by up to 12–13% with using the nanoporous GLAD Pt counter electrodes.     

Highly efficient all solid state dye-sensitized solar cells by the specific interaction of CuI with NCS groups II. Enhancement of the photovoltaic characteristics

Highly efficient all solid state dye-sensitized solar cells (DSSC) were fabricated by the specific interaction of CuI with the NCS groups of the dye molecules and that of the counter electrodes. The counter electrodes were prepared by blending nano size carbon in the PEDOT:PSS dispersion. The counter electrodes were covered with the solution containing guanidine thiocyanate, and heated to give the electrode with larger number of NCS groups. Electrostatic adsorption between PEDOT:PSS and guanidine was investigated by X-ray photoelectron spectroscopy (XPS). DSSC were prepared by connecting the NCS groups of the dye molecule with those of the counter electrode with large surface area. The performances of the resulting DSSC were improved dramatically by the increase of the NCS groups on the counter electrode. It is noteworthy that the performances of the cell were higher than that of the cells prepared by the conventional liquid electrolyte. The highly efficient all solid state DSSC are manufactured with inexpensive and low quality materials, and the practical use is promising.     

Carbon/carbon nanocomposites as counter electrodes for platinum free dye-sensitized solar cells

In this work, carbonaceous materials and their combinations with each other were used as counter electrodes for efficient dye-sensitized solar cells (DSSCs). A small amount of TiO₂ paste was also incorporated in each electrocatalyst to increase the adhesion between the carbon material and the conductive glass substrate. The dispersion of carbonaceous materials in composite films was characterized by transmission electron microscopy (TEM). Electrocatalytic characteristics of carbon/carbon catalysts are systematically investigated by electrochemical techniques, such as cyclic voltammetry and chronoamperometry. Solar cells assembled with carbon/carbon composite counter electrodes were characterized by photocurrent–voltage characteristic and electrochemical impedance spectroscopy measurements. The results indicate that under optimal conditions, the solar cell assembled with carbon/carbon composite counter electrode containing activated carbon, multi-walled carbon nanotube and graphene, shows power conversion efficiency of 10.73%. This photovoltaic performance is comparable with 11.20% for the platinum-based dye-sensitized solar cell. The results exhibit that carbonaceous material is an encouraging alternative for low-cost DSSCs.     

Vertically-oriented few-layer graphene supported by silicon microchannel plates as a counter electrode in dye-sensitized solar cells

Vertically-oriented few-layer graphene supported by silicon microchannel plates annealed at different temperatures are used in dye-sensitized solar cells (DSSCs). The structure, morphology, and electrochemical characteristics are determined by AFM, SEM, XPS, cyclic voltammetry, electrochemical impedance spectroscopy, and photocurrent density-voltage curves. The graphene/Si-MCP fabricated by electrochemical exfoliation delivers enhanced power conversion efficiency in DSSC and the materials annealed under ambient conditions at 300 °C show the best results due to the smaller oxygen concentration in graphene and larger electrical conductance. Owing to the microelectronics-compatible fabrication process and excellent properties of the device, the counter electrode has large potential in high-performance silicon-based monolithic DSSCs.     

The use of Ti meshes with self‐organized TiO2 nanotubes as photoanodes of all‐Ti dye‐sensitized solar cells

This paper reports a simple and facile method for directly growing self‐organized TiO₂ nanotubular arrays around the whole Ti mesh by electrochemical anodization in organic electrolytes and their application in all‐Ti dye‐sensitized solar cells (DSSCs). Compared with the traditional fluorine‐doped tin oxide (FTO)‐based DSSC and the backside illuminated DSSC, this type of DSSC showed advantages such as low resistance, cheap fabrication cost and enhanced sunlight utilization. Different thicknesses of nanotubular array layers were investigated to find their influence on the photovoltaic parameters of the cell. We also considered three types of meshes as the substrates of anodes and found that the cell with 6 openings/mm² exhibited the highest conversion efficiency of 5.3%. The area of the cell had only a little impact on the photovoltaic performances. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient monolithic solid-state dye-sensitized solar cell with a low-cost mesoscopic carbon based screen printable counter electrode

A low-cost mesoscopic carbon counter electrode (CE) with high surface area is applied in solid-state dye-sensitized solar cells (ss-DSCs) using spiro-OMeTAD hole transporting material (HTM). The intensity modulated photovoltage spectroscopy (IMVS) measurements are carried out to ascertain the thickness of insulating layer. The influence of mesoscopic carbon CE on the charge transfer process is characterized by the electrochemical impedance spectra (EIS) with CE/HTM/CE dummy symmetric cell, which indicates that the mesoscopic structure of CE is helpful to reduce the resistance of the interface between CE and HTM. A high efficiency up to 4.03% is obtained with D102 dye under 1 sun (AM1.5 global, 100 mW cm^?2), which is comparable to that of the conventional ss-DSC based on noble CE.     

In situ synthesis of CuS nano platelets on nano wall networks of Ni foam and its application as an efficient counter electrode for quantum dot sensitized solar cells

Herein, we report for the first time efficient CuS/nickel foam (NF) counter electrode for quantum dots-sensitized solar cells (QDSSCs) is fabricated using chemical bath deposition technique which can serve as a highly efficient CE for QDSSCs. These are characterized using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), current voltage and impedance spectroscopy. The CuS/NF and CuS/FTO films are investigated as a counter electrode (CE) in QDSSCs. The QDSSC based on CuS/NF CE achieves power conversion efficiency (PCE) of 4.93% accrediting to the high fill factor (FF) of 0.58, and the PCE is greater than that of CuS/FTO CE (4.27%) for TiO₂/CdS/CdSe/ZnS electrode, under the illumination of one sun (AM1.5, 100 mW cm⁻²). Electrochemical measurements testified that CuS/NF reveals high electro-catalytic activity towards polysulfide reduction, thus accelerating QDSSCs performance. Consequently, the CuS/NF is very capable as an efficient CE for QDSSCs. This procedure not only provides high electro catalytic activity but also an efficient scheme to be used in different applications such as flexible solar cells, fuel cells and supercapacitor.     

Novel development towards preparation of highly efficient ionic liquid based co-polymer electrolytes and its application in dye-sensitized solar cells

Ionic liquid polymer electrolytes (ILPE) were prepared with poly(1-vinylpyrrolidone-co-vinylacetate) P(VP-co-VAc) copolymer, tetrahexylammonium iodide (THAI) salt and 1-butyl-3-methylimidazolium iodide (BMII), a room temperature ionic liquid (RTIL). The ILPEs were characterized using electrochemical impedance spectroscopy (EIS) analysis, X-ray diffraction (XRD) studies, Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). The highest ionic conductivity obtained was 1.05 × 10⁻³ S cm⁻¹ at room temperature in ILPE3 which is the sample incorporated with 80 wt% of BMII. FTIR analysis proved the formation of complexes in between the copolymer, salt and ionic liquid. XRD studies have shown that ILPE3 has the optimum amorphous nature. The ILPE based dye sensitized solar cell (DSSC) was assembled by sandwiching the ILPE in between the nanoporous TiO₂ working electrode and Pt-coated counter electrode and thus subjected to device photovoltaic characterization. The DSSC with ILPE3 as its electrolyte has shown the highest power conversion efficiency (η) with a value of 4.93% with short circuit current density (J_sc), open circuit voltage (V_oc) and fill factor (FF) of 12.37 mA cm⁻², 0.69 V and 0.58, respectively. Temperature dependence studies has been done on the DSSCs to understand effect of the cell temperature on the performances of the DSSCs. EIS studies of the DSSCs shows that the ILPE is having higher diffusion coefficient compared to the GPE.     

Vertically aligned Ni3Se2 arrays with dendritic-like structure as efficient counter electrode of dye-sensitized solar cells

Fabrication of low-cost counter electrodes with high electrocatalytic performance is one of the most important challenges for dye-sensitized solar cells. Vertically aligned Ni₃Se₂ arrays with dendritic-like structure have been synthesized by a simple solvothermal method in this paper. Due to direct electron transfer and more catalytic active sites, Ni₃Se₂ arrays can be used as counter electrodes of dye-sensitized solar cells. The dye-sensitized solar cell based on Ni₃Se₂ array counter electrode shows a high photovoltaic performance with a high photoelectrical conversion efficiency of 4.62%, which is comparable with that of the dye-sensitized solar cell based on platinum counter electrode. To understand the chemical catalysis toward I₃^- reduction and interfacial charge transfer, the Ni₃Se₂ array counter electrode has been quantitatively investigated by the electrochemical measurements. The results indicate that the Ni₃Se₂ array counter electrode exhibits good catalytic activity and direct electron transfer for the reduction of I₃^-. Our research work will provide insight into the design and fabrication of counter electrode materials with high electrocatalytic performance for dye-sensitized solar cells.     

Metal oxide sandwiched dye-sensitized solar cells with enhanced power conversion efficiency fabricated by a facile and cost effective method

Developing efficient and cost effective photoanode and counter electro materials have been a persistent objective by a wide community for efficient, cost effective and stable dye-sensitized-solar cells (DSSCs). We have developed a unique and inexpensive way of co-electroplating-annealing method to synthesize metal oxides and employed it to prepare ZnO material on top of doctor bladed TiO₂ as photoanode and CuO on top of reduced graphene oxide (RGO) as counter electrode. By sandwiching these two electrodes with I^-/I₃ redox couple in-between we have shown the improvement of photovoltaic properties with ZnO barrier layer using Pt or cost effective CuO/RGO counter electrodes (CEs). This paper provides a comprehensive guide to prepare those electrodes cost effectively and fabricate metal oxide sandwiched DSSCs providing up to 6.91% power conversion efficiency with 26.5% enhancement compared to the conventional DSSCs with TiO₂ photoanode and Pt CE under AM1.5 simulated solar light. This work also addresses the reduction of fabrication cost of the cells to make them more economically viable as it is