Mitigating Defect States of All‐Inorganic CsPbI2Br Perovskite via Multifunctional 2‐Amino‐5‐Nitrothiazole Additive for an Efficient Air‐Processed Outdoor/Indoor Photovoltaics

All‐inorganic CsPbI 2 Br mixed halide perovskites show promise as wide‐bandgap photoabsorbers in photovoltaics. However, the rapid crystal growth observed in solution‐processed CsPbI 2 Br often leads to morphologies plagued by pinholes and defects, which limit device performance. This study introduces 2‐Amino‐5‐nitrothiazole (ANT), an innovative precursor additive, to enhance film quality. ANT's selective interactions with the perovskite precursor moderate the crystal growth, resulting in a dense, flawless CsPbI 2 Br film characterized by superior crystallinity and coverage. Furthermore, the NH 2 group in ANT coordinates with Pb octahedra, effectively mitigating charge defects through NHI/Br bonds. Simultaneously, SCN sites interact with uncoordinated Pb 2+ ions, reducing defect states and nonradiative recombination. This innovation achieves an impressive device efficiency of 17.13% with a fill factor (FF) of 83.41%, surpassing the control's efficiency of 15.21% (FF of 80.45%). Notably, the champion device maintains an efficiency of 29.47% under indoor light‐emitting diode lighting at 1000 lux. Additionally, the optimized perovskite solar cell demonstrates remarkable stability, retaining ≈90% of its efficiency for over 720 h at 85 °C in air, even without encapsulation.