染料敏化太阳能电池非铂对电极研究进展

对电极作为染料敏化太阳能电池（dye-sensitized solar cell,DSSC）的重要组成部分,对电极材料性能的好坏直接影响着染料敏化太阳能电池的光电转化效率。最常使用的对电极电催化材料是贵金属铂,而铂十分稀少而且价格昂贵,并且铂很容易被碘电解液腐蚀,不利于染料敏化太阳能电池的产业化发展。本文重点综述了2010年以来染料敏化太阳能电池非铂对电极的研究成果,简要说明了对电极在染料敏化太阳能电池中的作用,详细介绍了非铂金属、碳材料、导电聚合物和无机化合物等对电极材料,分析了各类非铂对电极材料的特点、制备工艺、发展前景、优缺点和改进措施。最后提出,继续开发各种成本低、原料易得以及稳定高效的新型非金属对电极材料仍是今后染料敏化太阳能电池研究的一个重要方向。     

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.     

A counter electrode of multi-wall carbon nanotubes decorated with tungsten sulfide used in dye-sensitized solar cells

Multi-wall carbon nanotubes decorated with tungsten sulfide (MWCNTs-WS₂) were synthesized by using a hydrothermal method, and used as a low-cost platinum-free counter electrode for dye-sensitized solar cell (DSSC). Cyclic voltammetry and electrochemical impedance spectroscopy characterizations indicate that the counter electrode has a high catalytic activity for the reduction of triiodide to iodide and a low charge transfer resistance at the electrolyte–electrode interface. A DSSC based on this counter electrode achieves a high power conversion efficiency of 6.41% under a simulated solar illumination of 100 mW cm⁻² (AM 1.5). This efficiency is comparable to 6.56% for a DSSC with Pt counter electrode.     

One- and two-dimensional carbon nanomaterials as counter electrodes for dye-sensitized solar cells

This study examines the dye-sensitized solar cells (DSSCs) equipped with 1-D carbon nanotubes (CNTs) and 2-D graphene nanosheets (GNs) carbon counter electrodes. Imperfect defects were attached to the sidewall or both the ends of the CNTs, and the edges of the GNs were analyzed by X-ray diffraction and Raman spectroscopy. When compared with the GN-based counter electrode, CNT-based counter electrodes showed a better improvement in the incident photon-to-current efficiency and power conversion efficiency of the cells. This enhancement of cell performance can be attributed to the combination of CNT network and spherical graphite bottom layer, favoring dye adsorption, catalytic redox activity, and 1-D charge-transfer path length. Such carbon configuration as counter electrode provides a potential feasibility for replacing metallic Pt counter electrodes.     

Enhanced efficiency of dye-sensitized solar cells with counter electrodes consisting of platinum nanoparticles and nanographites

The effect of a counter electrode (CE), fabricated by hybridizing the platinum nanoparticle (PtNP) and the nanographite (NG) on a dye-sensitized solar cell (DSSC), has been studied in this work. The catalytic PtNP/NG composite film for a CE is prepared using aniline (ANI) monomers as a dispersing medium, followed by spin-coating and annealing processes. The PtNP/NG composite film owns a high catalytic ability of converting tri-iodide to iodide due to the large surface roughness of the film. Thus, the DSSC assembled with the corresponding CE gives enhanced short-circuit current density (J_SC) and power-conversion efficiency (η) of 17.57 mA cm^?2 and 7.07%, respectively, while the corresponding values are 14.57 mA cm^?2 and 6.65% for a DSSC with a bare PtNP CE. Lower loading amounts of PtNPs for the PtNP/NG CE than those for the bare PtNP CE is demonstrated. Transmission electron microscopy (TEM) and UV/Vis absorption measurements are used to observe the dispersion of NGs in the solutions. X-ray diffraction (XRD) and Raman analyses are used to confirm the PtNP/NG composite film. The results are also substantiated by the characterizations of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electronic microscopy (SEM), and atomic force microscopy (AFM).     

Graphene aerogels as a highly efficient counter electrode material for dye-sensitized solar cells

Graphene aerogels (GAs) prepared with an organic sol–gel process, possessing a high specific surface area of 814 m²/g and a high electric conductivity of 850 S/m, are applied as a counter electrode material for dye-sensitized solar cells (DSSCs). The performance of the GA as the counter electrode material is found to be dependent on its film thickness, with thicker films offering more surface areas for the involved catalytic reduction reaction but at the same time increasing the charge and mass transport resistances. At an optimum GA film thickness of 4.9 μm, a power conversion efficiency of 96% of that achieved with a Pt counter electrode based DSSC is obtained. In addition, a thinner GA film of 1.7 μm, when loaded with Pt of 1 mol% through a photo-reduction process, achieves a power conversion efficiency of 98% of that obtained with a Pt counter electrode based DSSC. The excellent performances of the GA-based counter electrodes are manifested with electrochemical impedance analyses and cyclic voltammetry based catalytic activity analyses.     

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.     

Ferrocene-derivatized ordered mesoporous carbon as high performance counter electrodes for dye-sensitized solar cells

Ferrocene-derivatized large pore size mesocellular carbon foam (Fe-MCF-C) has been synthesized using divinylbenzene as a carbon source and mesocellular silica foam as a hard template. Cyclic voltammetric studies demonstrate a relatively faster electron transfer rate of Fe-MCF-C in K₃Fe(CN)₆/1 M KNO₃ solution, as compared with pristine mesocellular carbon foam (MCF-C). Such an enhanced electrochemical property is beneficial for improving the cathodic reduction of tri-iodide in dye-sensitized solar cells (DSSCs). Under 1 sun illumination (100 mW cm⁻², AM 1.5G), Fe-MCF-C counter electrode based DSSC shows an energy conversion efficiency of 7.89%, which is 12% higher than that of solar cell based on pristine MCF-C counter electrode.     

Nickel incorporated carbon nanotube/nanofiber composites as counter electrodes for dye-sensitized solar cells

A nickel incorporated carbon nanotube/nanofiber composite (Ni-CNT-CNF) was used as a low cost alternative to Pt as counter electrode (CE) for dye-sensitized solar cells (DSCs). Measurements based on energy dispersive X-rays spectroscopy (EDX) showed that the majority of the composite CE was carbon at 88.49 wt%, while the amount of Ni nanoparticles was about 11.51 wt%. Measurements based on electrochemical impedance spectroscopy (EIS) showed that the charge transfer resistance (R(ct)) of the Ni-CNT-CNF composite electrode was 0.71 Ω cm(2), much lower than that of the Pt electrode (1.81 Ω cm(2)). Such a low value of R(ct) indicated that the Ni-CNT-CNF composite carried a higher catalytic activity than the traditional Pt CE. By mixing with CNTs and Ni nanoparticles, series resistance (R(s)) of the Ni-CNT-CNF electrode was measured as 5.96 Ω cm(2), which was close to the R(s) of 5.77 Ω cm(2) of the Pt electrode, despite the significant difference in their thicknesses: ～22 μm for Ni-CNT-CNF composite, while ～40 nm for Pt film. This indicated that use of a thick layer (tens of microns) of Ni-CNT-CNF counter electrode does not add a significant amount of resistance to the total series resistance (R(s-tot)) in DSCs. The DSCs based on the Ni-CNT-CNF composite CEs yielded an efficiency of 7.96% with a short circuit current density (J(sc)) of 15.83 mA cm(-2), open circuit voltage (V(oc)) of 0.80 V, and fill factor (FF) of 0.63, which was comparable to the device based on Pt, that exhibited an efficiency of 8.32% with J(sc) of 15.01 mA cm(-2), V(oc) of 0.83, and FF of 0.67.     

Soft-template synthesized ordered mesoporous carbon counter electrodes for dye-sensitized solar cells

Ordered mesoporous carbon (OMC) with a high surface area (∼1575 m²/g) and bimodal pores (2.5 and 6.1 nm) was synthesized using a soft-template method employing triblock copolymer F127 as the structure directing agent and then applied as a low-temperature processable counter electrode for dye-sensitized solar cell (DSSC). The OMC counter electrode-based DSSC shows an energy conversion efficiency of 7.46%, whereas that of a Vulcan counter electrode is 4.30%. Electrochemical impedance spectroscopy analysis reveals decreased charge transfer resistance at the OMC counter electrode–electrolyte interface, thus improved fill factor and energy conversion efficiency.     

Prospects of conducting polymer and graphene as counter electrodes in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) garner considerable research interest because of high photo-to-electric conversion efficiencies at low production cost. Platinum has been reported as an efficient metal as a counter electrode (CE) in DSSCs for its outstanding electro catalytic performance. However, the high cost and susceptibility to corrosion of Pt are paving the way for exploring new materials to replace Pt as a counter electrode in DSSCs. Various conducting polymers, graphene and conducting polymer-graphene nanocomposites have been found as counter electrodes in DSSCs with remarkable photovoltaic performances. The urge to produce composites or hybrids with nanomaterials is derived from the improvement of photovoltaic performances. This review will focus on the unique physical and chemical properties of conducting polymers and graphene, their individual photovoltaic performances as counter electrodes in DSSCs, followed by the synergistic effect of conducting polymers and graphene in conducting polymer-graphene nanocomposites as counter electrodes in DSSCs. Finally a brief outlook is provided to improve the photovoltaic performance of DSSCs using conducting polymers and graphene-based counter electrodes.     

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%).     

9种树叶生物炭作为染料敏化太阳电池对电极的光电性能

将9种由树叶经单步热解获得的生物炭作为对电极催化材料引入染料敏化太阳电池（DSSC）,并在分析生物炭的组织结构和电化学性能的基础上,着重探讨了引起器件光电性能差异的内在原因。结果表明：9种树叶热解获得的生物炭组装的DSSC的转换效率在1.00%~1.85%之间,其中棕叶最佳,樟树叶和杨树叶其次,三者的转换效率均高于1.3%,随后依次为枫叶、红继木叶、椿树叶、杉树叶和松针,桂叶最低。生物炭的孔隙结构是引起相应器件光电性能各异的主要原因。由于棕叶生物炭具有独特的取向孔隙,能缩短电解质扩散距离以及提升催化活性,因此其器件的转换效率最佳。此外,9种生物炭器件的转换效率均高于石墨器件（0.77%）。更优的光电性能主要归功于生物炭具有的多级孔结构和玻璃态碳骨架。     

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.     

Polyaniline nanofiber/carbon film as flexible counter electrodes in platinum-free dye-sensitized solar cells

Efficient transfer of charges from a counter electrode to an electrolyte is a key process during the operation of dye-sensitized solar cells. Here, we develop a flexible counter electrode by electrochemical deposition of polyaniline nanofibers on graphitized polyimide carbon films for use in a tri-iodide reduction. As determined by the electrochemical impedance spectroscopy, the flexible counter electrode exhibited very low charge transfer resistance and series resistance. These results are due to the high electrocatalytic activity of the polyaniline nanofibers and the high conductivity of the flexible graphitized polyimide film. In combination with a dye-sensitized TiO₂ photoelectrode and electrolyte, the photovoltaic device with the polyaniline counter electrode shows an energy conversion efficiency of 6.85% under 1 sun illumination. Short-term stability tests indicate that the photovoltaic device with the polyaniline counter electrode almost maintains its initial performance.     

Graphene-based counter electrode for dye-sensitized solar cells

Graphene nanosheets (GNs) were synthesized and used as a substitute for platinum as counter-electrode materials for dye-sensitized solar cells (DSSCs). The as-synthesized GNs were dispersed in a mixture of terpineol and ethyl cellulose. GN films were screen-printed on fluorine-doped tin oxide (FTO) slides using the formed GN dispersions. GN counter-electrodes were produced by annealing the GN films at different temperatures. The annealed GN films revealed an unusual 3D network structure. Structural and electrochemical properties of the formed GN counter-electrodes were examined by field emission scanning electron microscopy, Raman spectroscopy and electrochemical impedance spectroscopy. It was found that the annealing temperature of GN materials played an important role in the quality of the GN counter-electrode and the photovoltaic performance of the resultant DSSC. The grown DSSCs with graphene-based counter-electrodes exhibited a conversion efficiency high up to 6.81%.     

Enhanced performance in dye-sensitized solar cells via carbon nanofibers-platinum composite counter electrodes

A composite counter electrode (CE) made of electrospun carbon nanofibers (ECNs) and platinum (Pt) nanoparticles has been demonstrated for the first time to improve the performance of dye-sensitized solar cells (DSCs). The new ECN-Pt composite CE exhibited a more efficient electro-catalytic performance with lower charge transfer resistance (R(ct)), larger surface area, and faster reaction rate than those of conventional Pt. It reduced the overall series resistance (R(se)), decreased dark saturation current density (J(0)) and increased shunt resistance (R(sh)) of the DSCs, thereby leading to a higher fill factor (FF) and larger open circuit voltage (V(oc)). The reduced electron transport resistance (R(s)) and faster charge transfer rate in the CE led to a smaller overall cell series resistance (R(se)) in the ECN-Pt composite based DSCs. The DSCs based on an ECN-Pt CE achieved a η of ～8%, which was improved over those of pure Pt or ECN based cells.     

Spray-deposited NiO x films on ITO substrates as photoactive electrodes for p-type dye-sensitized solar cells

Spray deposition followed by sintering of nickel oxide (NiO _x ) nanoparticles (average diameter: 40 nm) has been chosen as method of deposition of mesoporous NiO _x coatings onto indium tin oxide (ITO) substrates. This procedure allows the scalable preparation of NiO _x samples with large surface area (~10³ times the geometrical area) and its potential for applications such as electrocatalysis or electrochemical solar energy conversion, which require high electroactivity in confined systems. The potential of these NiO _x films as semiconducting cathodes for dye-sensitized solar cell (DSC) purposes has been evaluated for 0.3–3-μm-thick films of NiO _x sensitized with erythrosine B (ERY). The electrochemical processes involving the NiO _x coatings in the pristine and sensitized states were examined and indicated surface confinement as demonstrated by the linear dependence of the current densities with the scan rate of the cyclic voltammetry. Cathodic polarization of NiO _x on ITO can also lead to the irreversible reduction of the underlying ITO substrate because of the mesoporous nature of the sintered NiO _x film that allows the shunting of ITO to the electrolyte. ITO-based reduction processes alter irreversibly the properties of charge transfer through the ITO/NiO_x interface and limit the range of potential to NiO _x coatings sintered for DSC purposes.     

Fabrication and characterization of carbon-based counter electrodes prepared by electrophoretic deposition for dye-sensitized solar cells

Three different carbon-based counter electrodes are investigated in light of catalytic activities such as electrochemical frequencies and interface impedances. We fabricated carbon-based counter electrodes of dye-sensitized solar cells [DSSCs] using graphene, single-walled carbon nanotubes [SWNTs], and graphene-SWNT composites by electrophoretic deposition method. We observed the optical and electrochemical properties of the carbon-based counter electrodes. The DSSC with the graphene-deposited counter electrode demonstrated the best conversion efficiency of 5.87% under AM 1.5 and 1 sun condition. It could be utilized for a low-cost and high-throughput process for DSSCs.