Iodine Stabilization in Perovskite Lattice for Internal Stress Relief

Abstract Atomic iodine ionization in perovskite crystals leads to defect formation, lattice distortion, and the occurrence of localized micro‐strain. These atomic‐level chemical and mechanical effects significantly alter the electronic band landscape, profoundly affecting device performance. While iodine stabilization effects have traditionally been focused on stability, their impact on electrical properties, particularly the coupling effect with internal stress and lattice strain, remains underexplored. In this study, an iodine stabilization protocol using a parallel‐π‐stacked small molecule, [2,2]‐paracyclophane (PCP) is implemented, which plays a beneficial role in relieving internal stress within the perovskite lattice, thereby improving the film's electrical properties. By leveraging this iodine stabilization strategy, internal stress in the perovskite film, resulting in a strain‐free perovskite film and a corresponding device with an improved efficiency of 25.26% from 23.93% is successfully alleviated. The maximum power point tracking test of the perovskite device keeps 85% of its initial efficiency when illuminated under 1 sun for 1000 h, while the control device only maintains 57% of the initial efficiency under the same conditions. The good stability originates from the stable iodide ions in the perovskite lattice due to preventing iodide ions oxidation and perovskite degradation.