Intermediate Phase Modification Enables High‐Performance Iodine‐Rich Inorganic Perovskite Solar Cells with 3000‐Hour Stability

Abstract The presence of excess secondary‐phase PbI 2 in perovskite films shows a negative impact on their long‐term stability. Herein, an intermediate phase modification (IPM) strategy is proposed to eliminate residual PbI 2 for improved quality of all‐inorganic CsPbI 3 ‐type perovskite films, wherein the extrinsic agent is introduced to address the intermediate phase. By transforming residual PbI 2 into a novel 1D perovskite phase, the IPM strategy acts as a patch to suture grain boundaries in the inorganic perovskite films. In addition, the IPM strategy not only enhances the quality of perovskite films but also mitigates energy disorder, reduces trap state density, and prolongs carrier lifetime by expediting the intermediate phase conversion process and passivating surface defects. As such, the perovskite solar cells (PSCs) with a high power conversion efficiency (PCE) of ≈20% and a high fill factor of 83.3% are considered to be very efficient, with excellent shelf stability of 3000 h of exposure in air without any encapsulation. This work not only exhibits a novel optimization route for inorganic perovskite but also emphasizes the crucial role of eliminating residual PbI 2 in inorganic perovskites.