A simulation study of valence band offset engineering at the perovskite/Cu2ZnSn(Se1-xSx)4 interface for enhanced performance

Proper valence band offset at the perovskite/hole transport material interface is critical to obtain high performance perovskite solar cells. The Cu2ZnSn(Se1-xSx)4 compound is a potential candidate of hole transport material for perovskite solar cells and exhibits tunable band gap from 0.95 eV for Cu2ZnSnSe4 to 1.5 eV for Cu2ZnSnS4 with different S/(S+Se) ratio, which offers a feasible approach to engineering the valence band offset at the perovskite/Cu2ZnSn(Se1-xSx)4 interface. Here, the valence band offset engineering at the perovskite/Cu2ZnSn(Se1-xSx)4 interface is studied through numerical simulation with SCAPS package. The valence band offset can be tuned from negative value to positive value with different Cu2ZnSn(Se1-xSx)4 composition. With optimized S concentration, a suitable valence band offset (0.27 eV) is obtained, leading to a power conversion efficiency of 20.25%. Further optimization of thickness, defect density, and acceptor density of the Cu2ZnSn(Se1-xSx)4 transport layer is conducted, and power conversion efficiency of 20.77% is obtained. This study here provides a guidance to further optimize the performance of perovskite solar cells with Cu2ZnSn(Se1-xSx)4 hole transport material.