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

Tin dioxide (SnO₂) 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 SnO₂ 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 SnO₂. 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.