Dual‐Function Molecular Modulator Enables High‐Density Nucleation and Ordered Crystal Growth for Efficient Tin Perovskite Solar Cells

Tin perovskite solar cells (TPSCs) are considered a promising and environmentally friendly alternative to lead‐based perovskite photovoltaic devices. However, the uncontrollable crystallization kinetics of tin‐based perovskite often led to defective films, limiting the efficiency and stability of TPSCs. Herein, a dual‐functional 3‐furoic acid (3‐FA) is introduced as a crystallization modulator to decouple the nucleation and crystal‐growth processes. By coordinating with tin iodide (SnI 2 ) and simultaneously forming hydrogen bonds with formamidinium iodide (FAI), 3‐FA facilitates the formation of large‐size precursor complexes. These unique complexes effectively promote uniform, high‐density nucleation while enabling subsequent ordered perovskite crystal growth. The resulting high‐quality films exhibit enhanced crystallinity, highly uniform morphology, and a substantially reduced defect density. As a result, the 3‐FA modified devices exhibit simultaneous enhancements of open‐circuit voltage ( V OC ) and fill factor ( FF ), leading to a champion power conversion efficiency (PCE) of 16.16%. Furthermore, the devices demonstrate markedly improved thermal stability, retaining over 80% of their initial efficiency after 1150 h of aging at 60°C under a nitrogen atmosphere. This work provides a strategy that separates nucleation from crystal growth to overcome the longstanding challenge of crystallization control in tin‐based perovskites.