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

The unbalanced crystallization rate between Sn- and Pb-based perovskites leads to their heterogeneous distribution and inferior quality of Sn-Pb perovskite films. The promising strategy of selective molecular interaction would balance the crystallization rate. However, the deeper selectivity mechanism needs to be considered, particularly in terms of the entire coordination reaction in the perovskite precursor solution. Herein, we take advantage of thermodynamics and molecular orbital theory to reveal the competitive coordination of additive, i.e., methyl 5-aminolevulinate hydrochloride (5-AH), with SnI₂ and PbI₂. The SnI₂ competes with PbI₂ in coordinating with 5-AH to form the thermodynamically favored SnI₂-5-AH adducts with stronger SnI₂-Cl^-, thereby mediating the crystallization rate of the Sn- and Pb-based perovskite. Such crystallization regulation improves the composition uniformity and crystallization quality, which effectively suppresses nonradiative recombination. 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.