Buried SnI<sub>2</sub> Induces Gradient Heterojunctions in Sn–Pb Perovskite Solar Cells
Xue‐Wei Liu, Jia Xu, Chenxu Zhao, Fan Shen, Pengchen Zou, Yijun Wang, Baoping Ji, Xingjie Guan, Xu Pan, Jianxi Yao
Abstract
Tin–lead (Sn–Pb) mixed perovskite solar cells (PSCs) offer the potential for higher power conversion efficiency (PCE) than their pure lead counterparts. However, the lack of a well-defined Sn/Pb compositional profile results in disordered internal electric fields, limiting carrier separation. Here, we introduce a SnI 2 predeposition strategy that induces a vertical Sn/Pb composition gradient within the perovskite film. This gradient forms a continuous heterojunction, establishing a built-in electric field that enhances carrier separation and directional extraction. As a result, the optimized devices achieve a PCE of 23.2% along with improved stability, retaining 89.6% of their initial efficiency after 1032 h of storage in nitrogen. This work demonstrates a compositional and interfacial engineering approach for advancing the efficiency and durability of Sn–Pb mixed PSCs.