Inhibiting Buried Mechanical Failure via Vapor‐Induced Chemical Reconstruction for Durable Solar Cells

ABSTRACT Tin dioxide (SnO 2 ) is widely used as the electron transport layer (ETL) in n‐i‐p perovskite solar cells (PSCs) to achieve high efficiency. We reveal that reactive surface species on SnO 2 trigger a chemical degradation pathway that induces mechanical failure at the buried interface, which is manifested as cracks and voids. These volume defects severely impede charge‐carrier extraction and thus cause the degradation of PSCs under operational conditions. We report an effective ethanol vapor‐induced reconstruction (EVR) strategy that fundamentally modifies the surface chemistry of SnO 2 . This process converts the surface hydroxyl groups into a robust, covalently anchored acetate passivation layer via a facile gas‐solid reaction, simultaneously passivating the oxygen vacancies. The strategy effectively enhances the chemical stability of the buried interface and suppresses the generation of cracks and voids caused by light‐induced degradation. As a result, the optimized EVR n‐i‐p PSCs achieve a champion power conversion efficiency (PCE) of 26.19%. Furthermore, the EVR device showed improved stabilized power output and long‐term operational stability under light soaking, demonstrating the key role of robustness at the buried interface.