Preparation Of Transition Metal Sulfides-Based Thin Films For Counter Electrodes Of Dye-Sensitized Solar Cell

As an important part of the dye-sensitized solar cells（DSSCs）,the counter electrode（CE）plays an important role in the redox reaction of the electrolyte.Looking for a CE material that can replace noble metal Pt is an effective method to promote the further development of DSSCs.Compared to the research for new CE materials,how to improve the existing CE material with low activity is one of the important ways to obtain a low-cost and high-efficient CE.Among the CE materials that can replace Pt,transition metal sulfides have attracted much attention because of their advantages such as excellent electrocatalytic performance,abundant resources,low cost,and many kinds of elements.In this paper,from the perspective of adsorption energy optimization on electrocatalyst surface,the replacement of surface active sites of electrocatalysts,and industrialization production of DSSCs,the strategy of improving the electrocatalytic activity of transition metal sulfides CE and the preparation method of highly-active,flexible and large-scale Co S CE in DSSCs were explored.The specific research work is as follows:1.The strategy of using Co₃S₄ ultrathin active layer to significantly increase the electrocatalytic activity of inert Co₃O4 electrode was proposed.Theoretical calculations showed that the conversion of the inert Co₃O4 surface layer to Co₃S₄ can significantly increase its adsorption energy to the I atom（from 0.347 e V to 0.835 e V）,and increase its catalytic activity to the I-/I3-redox reaction;the experimental results showed that,with the rapid solution sulfuration method,only a 30 s sulfuration process can convert the Co₃O4 surface monolayer into active Co₃S₄,which greatly increased the electrocatalytic activity to the I3-reduction reaction.The DSSC test showed that the Co₃S₄/Co₃O4 composite electrode can exhibit similar CE activity to the traditional Pt electrode,and obtained power conversion efficiency of 8.6%.2.The effect of catalytic sites on the electrocatalytic activity of Cu2 XSn S₄ materials was investigated.The relatively sufficient research materials Cu2 Zn Sn S₄ CE was used as the object,the Zn element was replaced with the high electrocatalytic activity transition metal Co and Ni elements.The porous Cu2 XSn S₄ thin film was prepared by the sol-gel method.Studies showed that Cu2 Co Sn S₄ and Cu2 Ni Sn S₄ films exhibited higher I-/I3-electrocatalytic activity and stability compared to Cu2 Zn Sn S₄.The assembled DSSCs achieved a power conversion efficiency comparable to that of conventional Pt-based solar cells（8.3%）.Theoretical calculations indicated that this performance improvement is related to the balance of adsorption energy and desorption energy on CE surface.3.Explored low-temperature and large-area methods for preparing high-performance Co S CE.Co S powder was obtained by one-step ultrasonic spray pyrolysis method,which was further combined with PVDF and PEDOT:PSS polymer binders to achieve low temperature and large area（10×10 cm）highly active Co S CE.Studies showed that this new type of Co S-based CE material possessed comparable charge transfer resistance with that of conventional Pt.The assembled DSSCs achieved a power conversion efficiency of 8.8%.The multi-sampling test showed that the large area of the electrode showed a good position-electrocatalytic activity consistency.