Ternary Halogen Doping for Efficient and Stable Air‐Processed All‐Inorganic Perovskite Solar Cells

All‐inorganic CsPbI 3 perovskites have shown great promise in photovoltaic devices owing to their high theoretical power conversion efficiency (PCE) and excellent thermal stability compared to their organic–inorganic counterparts. However, due to the poor phase stability of CsPbI 3 perovskite under ambient conditions, it is still challenging to fabricate the efficient and stable all‐inorganic CsPbI 3 ‐based perovskite solar cells (PSCs). Herein, a ternary halogen doping strategy is demonstrated to improve the quality and stability of air‐processed all‐inorganic CsPbI 3 perovskite films, where CsBr and PbCl 2 are introduced as halide sources. Br and Cl are found to insert into the crystal lattice of the CsPbI 3 perovskite to improve its phase stability while regulating the crystallization process to improve its film morphology with reduced surface roughness and suppressed defect density. After optimizing the doping content of Br and Cl, the air‐fabricated PSC device based on ternary halogen doping yields a champion PCE of 17.51% with improved working stability, which retains over 80% of the initial PCE after continuous illumination for 2400 h. This work highlights the key role of halide‐doping in improving film quality and phase stability of air‐fabricated all‐inorganic perovskite, which is expected to promote the development of low‐cost and large‐scale production of all‐inorganic PSCs.