MoO2 Sacrificial Layer for Optimizing Back Contact Interface of Cu2ZnSn(S,Se)4 Solar Cells

The conversion efficiency of Cu ₂ ZnSn(S,Se) ₄ (CZTSSe) solar cells is relatively low, due to the complicated intrinsic defects and the unsuitable contact interfaces. In this work, MoO ₂ thin films prepared by a simple preannealing method are introduced to Mo/CZTSSe back contact interface. For the first time, it is found that MoO ₂ acts as a sacrificial layer rather than the traditional intermediate layer. Specifically, the MoO ₂ sacrificial layer will disappear and become a thin MoSe ₂ layer after it blocks the over-selenization of Mo electrode. In addition, it has a positive effect on the preferred orientation of MoSe ₂ and the crystallization of CZTSSe layer. Furthermore, the chemical mechanism on MoO ₂ as sacrificial layer is first investigated, and it can be well described by Van 't Hoff equation. With the aid of MoO ₂ sacrificial layer, the performance of CZTSSe device increases from 5.67% to 8.29% (active area efficiency is 9.08%) without the MgF ₂ antireflection layer.