Multifunctional Effects of Biguanide Derivative in the Application of Highly Efficient Tin‐Lead Perovskite Solar Cells

Abstract Tin‐lead (Sn‐Pb) mixed perovskites is beneficial to a single‐junction or all‐perovskite tandem device. However, the poor quality of the perovskite surface resulting from Sn 2+ oxidation and uncontrollable crystallization degrades device performance and stability. Herein, based on interface engineering, a novel biguanide derivative of PZBGACl is employed that integrates different types of N ‐related groups to reconstruct the surface/grain boundaries of Sn‐Pb perovskite. Combined with the microcorrosion effect of isopropanol solvent, PZBGACl can induce surface recrystallization of perovskite, and passivate various types of defects via hydrogen bond or Lewis acid‐base interaction, leading to an excellent perovskite film with reduced stress, larger grain size, and more n‐type surface. As a result, the obtained Sn‐Pb solar cell achieves a power conversion efficiency of 22.0%, and exhibits excellent N 2 storage/operation stability.