Effects Of Composition Regulation And Structure Optimization On The Performance Of Cu₂ZnSn（S,Se）₄ Thin Film Solar Cells

Cu₂Zn Sn（S,Se）₄（CZTSSe）solar cells are considered as the most promising thin film solar cells in the future due to the tunable band gap,high absorption coefficient,earth-abundant constituents,low cost,non-toxic,pollution-free and high stability.However,its highest efficiency is still far from that of Cu（In,Ga）Se₂solar cells.Studies have shown that the high-quality absorber layer and reasonable device structure are the basis for high-efficiency CZTSSe solar cells.In this thesis,the effect of cationic constituent regulation and the window layer on the photoelectric performance of CZTSSe solar cells are system studied.The main contents are as follows:1.The effect of finely tuned Zn/Sn ratio on the performance of CZTSSe films and their devices was well elucidated using a green and pollution-free dimethyl sulfoxide（DMSO）solution.From the analysis of the morphology,electrical conductivity,and device performance,it can be concluded that a slight change of Zn/Sn ratio will not lead to the generation of secondary phase.However,even a little change of Zn/Sn ratio will cause a great impact on the crystal quality of CZTSSe thin film.An appropriate Zn/Sn ratio can reduce the pores and bulk defects in the crystal so as to form a dense large-grain layer,suppress the probability of carrier recombination,increase the carrier concentration,and improve the electrical properties of the film.Through the regulation of Zn/Sn ratio,the short-circuit current density of CZTSSe-based solar cell increases from 35 to 36.45 m A/cm²,the fill factor is improved from 51.5%to 57.2%,and the photoelectric conversion efficiency reaches 8.82%from 7.59%.2.Two stable solutions of dimethyl sulfoxide and dimethylformamide（DMF）were used to prepare CZTSSe films by sol-gel method,and the function or role of i-Zn O layer exists in the traditional structure of CZTSSe solar cells was studied.The results show that the removal of i-Zn O layer will lead to a narrower depletion width and hence a decline of photogenerated current.However,the removal of i-Zn O layer can reduce the series resistance,thereby improving the fill factor of the CZTSSe solar cell.Based on our results,it can be concluded that removing the i-Zn O layer can improve the photoelectric conversion efficiency of CZTSSe solar cells.Then,the effect of ITO film thickness on the CZTSSe thin film solar cells with a i-Zn O free structure was systematically explored.Through the optimization of the ITO window layer,the utilization of sunlight increases and more photogenerated carriers are obtained,which is beneficial to improve the performance of CZTSSe solar cells.The best photoelectric conversion efficiency is over 10%for the CZTSSe thin-film solar cells in both DMSO and DMF systems.