In Situ Dual‐Interface Passivation Strategy Enables The Efficiency of Formamidinium Perovskite Solar Cells Over 25%

Abstract Perovskite solar cells (PSCs) are promising candidates for next‐generation photovoltaics owing to their unparalleled power conversion efficiencies (PCEs). Currently, approaches to further improve device efficiencies tend to focus on the passivation of interfacial defects. Although various strategies have been developed to mitigate these defects, many involve complex and time‐consuming post‐treatment processes, thereby hindering their widespread adoption in commercial applications. In this work, a concise but efficient in situ dual‐interface passivation strategy is developed wherein 1‐butyl‐3‐methylimidazolium methanesulfonate (MS) is employed as a precursor additive. During perovskite crystallization, MS can either be enriched downward through precipitation with SnO₂, or can be aggregated upward through lattice extrusion. These self‐assembled MS species play a significant role in passivating the defect interfaces, thereby reducing nonradiative recombination losses, and promoting more efficient charge extraction. As a result, a PCE >25% (certified PCE of 24.84%) is achieved with substantially improved long‐term storage and photothermal stabilities. This strategy provides valuable insights into interfacial passivation and holds promise for the industrialization of PSCs.