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

Scalable fabrication of tin-based perovskite solar cells (TPSCs) remains challenging due to rapid crystallization, poor film uniformity, and instability of Sn2+. 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 SnI2 in governing crystallization kinetics, where pre-formed crystalline SnI2 hinders cation diffusion, while amorphous SnI2 promotes homogeneous film growth. Additive engineering with guanidinium iodide (GAI), SnF2, and trimethylene sulfoxide (TMSO) improved crystallinity, suppressed Sn2 + 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 SnI2 and provides a scalable pathway toward efficient, stable, and lead-free perovskite photovoltaics.