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 (ACN), 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% relative humidity [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.