MoO<sub>2</sub> Sacrificial Layer for Optimizing Back Contact Interface of Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub> Solar Cells
Bin Xu, Xiaoshuang Lu, Chuanhe Ma, Yulin Liu, Ruijuan Qi, Rong Huang, Ye Chen, Pingxiong Yang, Junhao Chu, Lin Sun
Abstract
The conversion efficiency of Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ZnSn(S,Se) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (CZTSSe) solar cells is relatively low, due to the complicated intrinsic defects and the unsuitable contact interfaces. In this work, MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> acts as a sacrificial layer rather than the traditional intermediate layer. Specifically, the MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sacrificial layer will disappear and become a thin MoSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer after it blocks the over-selenization of Mo electrode. In addition, it has a positive effect on the preferred orientation of MoSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and the crystallization of CZTSSe layer. Furthermore, the chemical mechanism on MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as sacrificial layer is first investigated, and it can be well described by Van 't Hoff equation. With the aid of MoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sacrificial layer, the performance of CZTSSe device increases from 5.67% to 8.29% (active area efficiency is 9.08%) without the MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> antireflection layer.