Hyperactive Selenium Source Yields Kesterite Solar Cells with 12.86% Efficiency

Abstract

AbstractOne 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 Cu2‐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 CuZn and SnZn defects, as well as [2CuZn + SnZn] 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.