Research On Dye-sensitized Solar Cells Based On The Transition Metal Counter Electrodes

Dye-sensitized solar cells（DSSCs）are the new type of solar cells with the most market potential.The counter electrode is one of the important parts of the DSSCs,its performance directly affects the power conversion efficiency of the DSSCs.The platinum is commonly used as counter electrode catalytic material due to excellent catalytic activity and conductivity.In view of the fact that platinum is precious metal and its storage capacity is limited,it is not conducive to the industrial production of DSSCs.Therefore,it is of great significance to develop low-cost non-platinum counter electrode materials.In this paper,two kinds of non-platinum counter electrode materials the VS₂ and CuMnSnS₄ doped with carbon nanotubes（CNTs）were introduced,their catalytic and optoelectronic properties in DSSCs were studied.The specific research work is as follows:（1）Different temperature of VS₂ were synthesized by using a simple in situ hydrothermal route, which was used as non-platinum counter electrodes for the first time.The surface morphology,elemental composition and crystal structure of the VS₂ samples were characterized by using SEM,EDS,XRD and TEM.The SEM showed that the morphology of VS₂ were affected by temperature,the size of the VS₂increased with the increasing of temperature and the nanoparticles transformed into a one-dimensional（1D）structure.The results showed that the VS₂ nanofibers prepared at 180°C had a larger specific surface area.This structure was conducive to improve the adsorption of more electrolytes,the contact frequency of electrolyte and counter electrodes and the reduction rate of I₃^-.Extensive electrochemical performance analysis including cyclic voltammetry（CV）,electrochemical impedance spectroscopy（EIS）and Tafel curves revealed that the VS₂ counter electrode prepared at 180°C had excellent electrocatalytic activity,rapidly reduced triiodide（I₃^-）to iodide（I^-）,and a lower charge transfer resistance at the electrolyte and counter electrode interface.Compared to the DSSC based on the Pt counter electrode,the DSSC based on the VS₂ counter electrode showed a photoelectric conversion efficiency of 6.24%under illumination of 100mW·cm^-2,which was almost similar to that of the Pt-based cell（6.44%）.（2）The DSSC based on the pure VS₂ counter electrode has a slightly lower photoelectric conversion efficiency（PCE）than that of the DSSC based on the platinum electrode.In order to improve the photoelectric properties of the device,the CNTs with good conductivity were doped in the precursor solution of the VS₂.Extensive electrochemical tests were used to explore the influence of the doping amount with CNTs on the electrocatalytic activity of CNTs/VS₂ electrodes,and these results showed that the CNTs/VS₂ doped with 0.05 g CNTs possesses the best catalytic performance.In addition,the photocurrent-voltage（J-V）curves showed DSSC based on the CNTs/VS₂ counter electrode prepared by using in situ hydrothermal route at 180°C and contained 0.05 g CNTs,which showed 8.02%high photoelectric conversion efficiency under 100 mW·cm^-2 illumination.Compared to the DSSC（6.49%）based on the platinum electrode,the photoelectric conversion efficiency is significantly improved by 23.5%,which mainly due to the unique structure and good physical and chemical properties of the CNTs.（3）The high efficiency hybrid counter electrodes of CuMnSnS₄（CMTS）/CNTs（CMTS/CNTs） were prepared by using in situ hydrothermal route.The crystal structure,elemental composition and surface morphology of the CMTS/CNTs samples were characterized by XRD,EDS,TEM and SEM.The SEM showed that the CNTs distributed uniformly in the CMTS nanoflowers and formed a new microsphere.The extensive electrichemical characterizations including cyclic voltammetry,electrochemical impedance and Tafel curves for the CMTS/CNTs were implemented,they showed better electrocatalytic activity and lower charge transfer resistance at the electrolyte and counter electrode interface for I^-/I₃^-liquid electrolyte.The J-V curves showed that the DSSC based on the CMTS/CNTs counter electrode contained 0.05 g CNTs exhibited a photoelectric conversion efficiency of 8.97%under illumination of 100 mW·cm^-2.