3D Interaction of Zwitterions for Highly Stable and Efficient Inorganic CsPbI₃ Solar Cells

Abstract All‐inorganic cesium lead iodide (CsPbI₃) perovskites, which replace volatile and hygroscopic organic components with stable inorganic cesium cations, have promising photoelectronic properties for potential application in solar cells. However, highly stable and efficient CsPbI₃‐based perovskite solar cells are rarely reported because the optically active black phases of CsPbI₃ tend to change into a photo‐inactive yellow δ‐phase. Herein, a highly stable CsPbI₃ film that is formed by introducing a small quantity of zwitterions with different dimensions to the perovskite precursor solution is reported. The zwitterions effectively inhibit the formation of the yellow δ‐phase during perovskite crystallization and promote the development of a stable black α‐phase. In addition, a systematic analysis reveals strong interaction between 3D zwitterions and perovskites in both the solution and film states, which leads to a dense and pinhole‐free CsPbI₃ film with suppressed trap states. The resulting perovskite solar cells with 3D zwitterions achieve a significantly improved power conversion efficiency of 18.4% with high reproducibility. The devices without encapsulation retain 98% of the initial efficiency after 25 days at 25 °C and relative humidity of 25% ± 5%. Importantly, the 3D zwitterion‐based devices demonstrate excellent phase stability when subjected to thermal aging at 100 °C.