In Situ Stabilized CsPbI₃ for Air-Fabricated Inverted Inorganic Perovskite Photovoltaics with Wide Humidity Operating Window

Inverted triiodine cesium lead (CsPbI₃) perovskite solar cells (PSCs) are promising in photovoltaics owing to their ideal light absorption, non-volatile active layer, and avoidance of fragile Spiro-OmeTAD, especially as the top cell in tandem devices. However, they still exhibit far-lagging efficiency, and must be processed in a strictly controlled environment due to water-fearing CsPbI₃. Here, a novel strategy to convert the harmful water erosions into an in situ stabilizer for efficient inverted CsPbI₃ PSCs fabricated with a wide humidity operating window, is proposed. During air fabrication, maleic anhydride (MAAD) can react with water molecules in air to reduce moisture erosions, while the hydrolysis products (maleic acid, MAAC) control grains growth. After annealing, MAAC strongly binds to CsPbI₃ grains as a shield to hamper phase transition and moisture penetration. A champion efficiency of 19.25% is obtained, which is the highest efficiency among the inverted inorganic PSCs. In parallel, the authors’ optimized devices present efficiency of 18.39% even fabricated in relative humidity 60% condition. Moreover, the stability against various ages is improved, and the optimized devices remain at 96.8% of its initial efficiency after maximum power point tracking at 65 °C for 850 h.