Novel buffer layer on the performance of CZTS solar cells by numerical simulation

Cu2ZnSnS4 as the promising absorber layer material, has received great attention in the application of highly efficient and low-cost thin film solar cells. The theoretical photovoltaic conversion efficiency of the CZTS thinfilm solar cells reaches up to around 32%. Conventionally, CdS or CdSe have been used as buffer layers in these cells. However, cadmium's toxicity and volatility pose environmental concerns. This paper explores TiNxOy and CrNxOy as buffer layers in CZTS solar cells, investigated through numerical simulations using SCAPS-1D. Thickness and carrier concentration on the solar cell performance are mainly investigated. Effects of conduction band offset and defect density on photovoltaic parameters of CZTS/TiNxOy and CZTS/CrNxOy solar cells are also simulated based on the optimal thickness and carrier concentration. The simulation results point out that the photovoltaic conversion efficiency of both systems achieves 22% when TiNxOy or CrNxOy is used as buffer layers. Notably, compared with the CZTS/CrNxOy solar cell structure, TiNxOy as the buffer layer provides a more compatible band offset with the CZTS layer.