Overcoming Back Interfacial Barrier Improves Flexible Cu2ZnSn(S,Se)4 Solar Cell Efficiency via CuO Sacrificial Layers

The optimization of the back interface is an important means of improving the power conversion efficiency (PCE) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Here, a CuO sacrificial layer is introduced into the Mo/CZTSSe back interface to improve device efficiency. The insertion of the CuO sacrificial layer inhibits the formation of Sn(S,Se)2 secondary phases in the CZTSSe film. Meanwhile, the interfacial trap state (NIT) is reduced by about 22%. Furthermore, the 75 nm CuO sacrificial layer can reduce the thickness of the MoSe2 layer, leading to a 33.18 meV reduction in the back interfacial barrier. This design enhances the back interfacial transport characteristics and suppresses defects. Finally, the flexible CZTSSe solar cell achieve the efficiency of 10.57%.