Dual‐Coordinated Additive Ameliorates Crystallization Kinetics and Charge Transport of Tin Halide Perovskite Solar Cells

Abstract Tin halide perovskites face with grand challenges in versatile applications due to their over‐fast crystallization from the high Lewis acidity of Sn 2+ and severe p‐doping from the Sn 2+ oxidation. This study explores a Lewis‐base additive dicyandiamide (DCD), which achieves precise molecular structural matching with tin perovskite lattices through creating dual‐coordinated Sn←N and N─H⋯I bonds with halide perovskites. Such a molecular mechanism decelerates crystallization kinetics and stabilizes intermediate phases, thereby promoting the formation of dense and low‐defect THP films. DCD also acts to passivate Sn 2+ /I − defects, suppress Sn 2+ oxidation, and reduce non‐radiative recombination. Directional coordination of DCD minimizes self‐aggregation and enhances interfacial charge transfer, overcoming the intrinsic restriction of conventional additives. The optimized Sn‐based perovskite solar cell devices exhibit simultaneous enhancements of all photovoltaic parameters, leading to a remarkable leap in power conversion efficiency from 13.05% (control) to 15.45% (champion). Notably, the unencapsulated DCD‐modified devices maintain 80% of their initial efficiency after 3100 h storage in an Ar atmosphere. This work offers a facile dual‐strategy of crystallization control and defect passivation in advancing eco‐friendly perovskite photovoltaics.