Photovolatic Performance And Modification Of TiO₂ Photoanode For Dye-Sensitized Solar Cell

Providing clean and sustainable energy is now becoming more essential because of the global decline of fossil fuels in the last decades.The high consumption of fossil fuels leads to an increase in carbon dioxide emissions in the environment and global warming.This global challenge can be mitigated by the introduction of low cost,renewable and sustainable energy sources and technologies.It is important to note that the access of economically viable renewable and sustainable energy is vital for the environment and society development.The widely available renewable and green energy resources are solar,wind,hydropower,geothermal and biomass as compared to other resources that are not evenly distributed.Among them,the most widely available resource is the solar radiation and is projected to perform a vital role in the future energy demand.Dye sensitized solar cells（DSSCs）are one of the most effective devices for converting solar energy into electrical energy,and their emergence has aroused great interest among the researchers.In DSSCs,photoanode materials is a bridge connecting dyes and conductive substrates,which is of great significance for the rapid transmission of electrons.TiO₂is considered the best choice for DSSCs photoanode materials due to its large bandgap,suitable edge positions for charge injection and extraction,long lifetime of excited electrons,excellent photo corrosion resistance,non-toxicity,and low cost.In nanostructured titanium dioxide materials,mesoporous TiO₂ nanocrystalline particles have attracted much attention due to their large specific surface area,which can enhance the reaction at the interface between the photoanode and the interacting medium,thereby improving the photoelectric conversion efficiency of DSSCs.However,the lower electron mobility of TiO₂ and the electron trap state at the grain boundary of nanocrystalline particles increase the recombination loss of photogenerated carriers at the internal interface of DSSCs.In response to the above constraints,focusing on improving the photoelectric conversion efficiency of DSSCs,we have studied the doping modification and structural optimization of TiO₂photoanode.The specific contents are as follows:A series of Sn-doped TiO₂ nanocrystals with Sn content ranging from 0 to 4 at.%were successfully synthesized by the hydrothermal method,and its performance as the photoanode of dye-sensitized solar cells（DSSCs）was investigated.The XRD results indicate that the doping has no effect on the crystal structure of TiO₂.The shift of XRD and Raman peaks observed at lower angle and the XPS results indicate that Sn⁴⁺ions incorporation into the TiO₂ lattice.The flatband potential of Sn-doped TiO₂ films shifts to a more negative position with increasing Sn content from 0 to 4 at.%,which is beneficial to the increase of V_oc of DSSCs.In addition,the electron lifetime（?_e）in undoped and Sn-doped TiO₂ based DSSCs shows that Sn doping can improve the electron mobility of TiO₂,and thus improve the short-circuit current density(J_sc)of DSSCs.Based on this,the optimum efficiency of 7.70%was found at 2 at.%Sn-doped TiO₂ based DSSCs,which gave an efficiency improved by 32.7%compared with that of the cells based on pure TiO₂.TiO₂ nanowire arrays were prepared by the hydrothermal method,and Zn S passivation modified TiO₂ nanowire arrays were prepared by continuous ion layer adsorption and reaction methods.The characterization results of XRD,SEM,TEM,and XPS indicate that Zn S passivation modification has no significant effect on the morphology and crystal structure of TiO₂ nanowire arrays.DSSCs were prepared using TiO₂ nanowire arrays with different Zn S passivation modifications as photoanodes,and the effect of Zn S passivation modification on the photoelectric conversion performance of DSSCs was analyzed.The results show that the addition of Zn S increases the electron density in the TiO₂ conduction band,thereby improving the V_ocvalue of the devices.Meanwhile,the presence of Zn S passivation layer can effectively prevent electronic recombination between the interfaces in DSSCs and improve the J_scvalue of the devices.DSSCs were prepared using Zn S passivation modified TiO₂nanowire arrays under optimized conditions.The J_sc and V_oc of the device are increased to 17.37 m A cm^-2 and 784 m V,respectively.The photoelectric conversion efficiency of the cell reaches 10.43%.