Hyperactive Selenium Source Yields Kesterite Solar Cells with 12.86% Efficiency
Mengyang Wang, Hang Geng, Jichun Zhu, Yubo Cui, Shanheng Zhao, Junjie Fu, Dongxing Kou, Jie Sun, Chaoliang Zhao, Sixin Wu, Liming Ding, Zhi Zheng
Abstract
Abstract One of the main issues that limits the efficiency of kesterite solar cells is the low diffusion and chemical activity of selenium clusters. Here, this work proposes a simple and effective pre‐selenization strategy using Na 2 (Se 2 S) solution, which enables the direct introduction of hyperactive Se 2 , Se 3 , and Se 4 into the precursors. The results demonstrate that Se 2 , Se 3 , and Se 4 promote the formation of the Cu 2‐x Se liquid phase and enhance the diffusion of elements from different micro‐regions. Consequently, the ratios of Cu/(Zn + Sn) and Sn/Zn in different micro‐regions of the absorber are controlled within the optimal range, exhibiting reduced fluctuations. The controlled environment suppresses the formation of Cu Zn and Sn Zn defects, as well as [2Cu Zn + Sn Zn ] defect clusters. Finally, a power conversion efficiency (PCE) of 12.86% is achieved, which is the highest PCE for kesterite solar cells made under ambient pressure and with N,N‐ dimethylformamide solvent.