Competitive Coordination Induced Crystallization Regulation for Efficient and Stable Sn-Pb Perovskite Solar Cells

Abstract

The faster crystallization rate of Sn perovskite compared with Pb perovskite leads to the spatial component inhomogeneity and inferior quality of the Sn-Pb perovskite films, which increases the quasi-Fermi level splitting (QFLS) deficit and accelerates the oxidative degradation of the films, thus undercutting the efficiency and stability of Sn-Pb perovskite solar cells. Herein, we propose a thermodynamic selective strategy to mediate the crystallization rate between the Sn- and Pb-based perovskite by introducing methyl 5-aminolevulinate hydrochloride (5-AH) in perovskite precursor solution. The SnI2 competes with PbI2 in coordinating with 5-AH to form the thermodynamically favored SnI2-5-AH adducts with stronger SnI2-Cl− according to molecular orbital interactions, thereby delaying the crystallization of Sn-based perovskite. Such crystallization regulation improves the composition uniformity and the crystallization quality, which effectively suppresses non-radiative recombination and reduces the QFLS deficit. Additionally, the strong interaction between Sn2+ and 5-AH as well as reductive grain boundaries inhibits the oxidation of Sn2+. Therefore, the optimal devices with 5-AH exhibit an improved PCE of 23.76% with a high voltage of 0.885 V and long-term stability, maintaining 89% of initial efficiency under continuous irradiation for 1100 h at the maximum power point under AM 1.5G.