Hyperactive Selenium Source Yields Kesterite Solar Cells with 12.86% Efficiency

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 Na₂(Se₂S) solution, which enables the direct introduction of hyperactive Se₂, Se₃, and Se₄ into the precursors. The results demonstrate that Se₂, Se₃, and Se₄ promote the formation of the Cu_2‐xSe 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.