In situ Cation Exchange Enables Air‐Processed Inverted Perovskite Solar Cells with Over 25% Efficiency and Enhanced Stability

The scalable fabrication of inverted perovskite solar cells (IPSCs) in humid air with an antisolvent‐free process is essential for future industrial applications. However, high humidity poses significant challenges for achieving high‐quality perovskite films, making it difficult to attain efficient IPSCs under ambient conditions. Here, we present an in situ cation exchange strategy to create a compact and uniform PbI2 shell on the perovskite surface by using ZnI2 in acetonitrile, where Zn2+ replaces Pb2+. This transformation is attributed to the surface defects of the perovskite, which undergo a cation exchange reaction in humid air, forming a compact PbI2 shell. The n‐type PbI2 shell effectively encapsulates the perovskite films, minimizing air exposure while optimizing energy level alignment, thereby enhancing electron transport and extraction. As a result, we demonstrate IPSCs with efficiencies of 25.2% under ambient conditions (25–30°C, 60 ± 10% RH), on par with state‐of‐the‐art devices fabricated in inert atmospheres. The devices demonstrated remarkable stability, enduring aging tests under the International Summit on Organic Photovoltaic Stability (ISOS) protocols ISOS‐D‐1I and ISOS‐D‐2I for over 4770 and 2000 h, respectively.