MoO₂Sacrificial Layer for Optimizing Back Contact Interface of Cu₂ZnSn(S,Se)₄Solar Cells

The conversion efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is relatively low, due to the complicated intrinsic defects and the unsuitable contact interfaces. In this work, MoO2 thin films prepared by a simple preannealing method are introduced to Mo/CZTSSe back contact interface. For the first time, it is found that MoO2 acts as a sacrificial layer rather than the traditional intermediate layer. Specifically, the MoO2 sacrificial layer will disappear and become a thin MoSe2 layer after it blocks the over-selenization of Mo electrode. In addition, it has a positive effect on the preferred orientation of MoSe2 and the crystallization of CZTSSe layer. Furthermore, the chemical mechanism on MoO2 as sacrificial layer is first investigated, and it can be well described by Van 't Hoff equation. With the aid of MoO2 sacrificial layer, the performance of CZTSSe device increases from 5.67% to 8.29% (active area efficiency is 9.08%) without the MgF2 antireflection layer.