Enhanced Photovoltaic Performance of Lead‐Free Perovskite Solar Cells With Volatilizable Solvent

Tin‐based perovskite solar cells (Sn‐PSCs) represent the most efficient lead‐free alternative to conventional lead‐halide PSCs, but their performance is limited by rapid crystallization and poor film morphology. Here, we introduce ethyl propyl sulfide (EPS) as a multifunctional volatile additive to modulate the formation of tin perovskite (Sn‐PVK) films. EPS is designed to evaporate during thermal annealing after having exerted its coordination effects, leaving no residues in the final film. The sulfur atoms in EPS strongly coordinate with Sn 2+ , forming an intermediate complex that retards crystallization and suppresses the oxidation of Sn 2+ . This process yields highly crystalline Sn‐PVK films with a trap density reduced by an order of magnitude, indicating slowed transformation kinetics during deposition. As a result, the power conversion efficiency of Sn‐PSCs increases from 11.02% to 12.44%, accompanied by enhanced device stability. This study highlights the importance of combining volatility and strong coordination in molecular design for efficient and stable Sn‐PSCs.