Surface Solvent Cleaning-Assisted Vapor-Phase Passivation Strategies for High-Quality Perovskite Thin Films Grown by Vapor–Solid Reaction

Perovskite films grown by a vapor–solid reaction are highly attractive due to their exceptional process controllability and industrial potential. A key feature of the vapor–solid approach is that the reaction initiates at the surface and progressively penetrates the film, often yielding an excess of surface formamidinium cations (FA + ) and disrupting the stoichiometry. This imbalance hinders subsequent surface passivation and ultimately constrains device performance. Here, we introduce a solvent-cleaning–assisted vapor-phase passivation strategy with synergistic surface engineering. First, isopropanol washing selectively removes excess surface FA + to tailor the surface chemistry, followed by vapor-phase passivation using phenethylammonium iodide (PEAI). This coordinated process promotes the reconstruction of the perovskite surface and effectively passivates surface defects, producing high-quality films. Working with these films, inverted-structure perovskite solar cells show a notable efficiency boost from 18.17% to 20.70% (0.148 cm 2 ), with larger-area devices (1 × 1 cm 2 ) achieving 18.42%. Additionally, unencapsulated devices retain over 90% of their initial efficiency after 1500 h, indicating strong interfacial stability. This study demonstrates a practical route to actively regulate the surface chemical environment of vapor–solid-grown perovskite films and offers a reference point for the future development of vapor-phase passivation strategies in perovskite technology.