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 (μ I ) to precisely manage point defects remains unexplored. Here, we combine DFT calculations with an innovative I 2 sublimation strategy to adjust μ I in CsPbIBr 2 films, intentionally introducing interstitial iodine (I i ) defects. DFT shows a broad chemical window for iodine, allowing significant tunability, while I-rich conditions promote I i formation, though excessive levels risk CsPbI 2 Br phase segregation. Experimentally, a 2 min I 2 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 × 10 13 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.