Chemical-Potential-Guided Iodine Treatment Converts Iodine Vacancies into Interstitial Defects for High-Performance Perovskite Photodetectors via Photoremediation

Despite the promising optoelectronic properties of all-inorganic perovskites, their performance is limited by intrinsic defect-mediated recombination and phase instability under iodine-rich conditions. While previous studies have focused on additive engineering and interface modifications to control crystallization or reduce defects, direct manipulation of the halide chemical potential (μI) to precisely manage point defects remains unexplored. Here, we combine DFT calculations with an innovative I2 sublimation strategy to adjust μI in CsPbIBr2 films, intentionally introducing interstitial iodine (Ii) defects. DFT shows a broad chemical window for iodine, allowing significant tunability, while I-rich conditions promote Ii formation, though excessive levels risk CsPbI2Br phase segregation. Experimentally, a 2 min I2 treatment optimally enhances PL intensity and induces notable light-induced PL improvements, attributed to reduced defect density and increased carrier lifetime. This suppression of nonradiative recombination results in a photodetector with a responsivity of 0.29 A W–1 and a specific detectivity of 1.79 × 1013 Jones, representing a 16% increase in responsivity and a 10-fold improvement in detectivity. The mechanism involves migration of I– to iodine vacancies, facilitating defect elimination. This work offers a defect engineering approach through chemical potential control for advanced perovskite optoelectronics.