Synergistic Additive and Bulky Cation Engineering via a Sequential Vacuum Dry‐Dipping Process for Tin Perovskite Solar Cells

ABSTRACT Scalable fabrication of tin‐based perovskite solar cells (TPSCs) remains challenging due to rapid crystallization, poor film uniformity, and instability of Sn 2+ . Herein, we report a spin‐coating‐free approach, combining blade coating, vacuum‐drying, and controlled dipping methods, to achieve highly crystalline and uniform tin perovskite films. Through systematic studies, we reveal the universal role of SnI 2 in governing crystallization kinetics, where pre‐formed crystalline SnI 2 hinders cation diffusion, while amorphous SnI 2 promotes homogeneous film growth. Additive engineering with guanidinium iodide (GAI), SnF 2 , and trimethylene sulfoxide (TMSO) improved crystallinity, suppressed Sn 2 + oxidation, and extended carrier lifetimes. Moreover, we introduce n‐butylammonium tosylate (BATo) as a dual‐functional bulky cation, whose BA + group enhances lattice ordering while the tosylate (TsO − ) group passivates buried interfaces. Compared with conventional blade‐coating and spin‐coating methods, the dipping process facilitates the penetration of large molecules into the film and further enables lattice reconstruction. Devices incorporating BATo achieved a power conversion efficiency (PCE) of 10.2%, retained >90% efficiency under continuous operation, and maintained >80% after 2500 h of shelf storage. This work clarifies the intrinsic role of SnI 2 and provides a scalable pathway toward efficient, stable, and lead‐free perovskite photovoltaics.