Enhancing Photostability of All‐Inorganic Perovskites via Natural Antioxidant Passivation for High‐Performance Fluorescent Sensors

All‐inorganic CsPbBr 3 perovskites exhibit excellent optical performance but suffer from severe instability under ultraviolet (UV) radiation. Here, we report a green and facile strategy to enhance their UV stability by introducing natural antioxidant lycopene (LP). As a Lewis base, LP provides a hydrophobic π‐conjugated barrier that suppresses moisture penetration, while its conjugated chain and photo‐oxidized C = O group dynamically passivate uncoordinated Pb 2+ and inhibit the migration of Br − . Consequently, the treated CsPbBr 3 retains 80% of its initial emission intensity after 200 h of continuous UV exposure, compared to complete quenching within 20 h for untreated CsPbBr 3 . After further characterization and stability testing, it was found that LP produced similarly outstanding results in the CsPb(Br 0.5 Cl 0.5 ) 3 . Based on this enhanced photostability, a dual‐channel UV fluorescence sensor using treated CsPbBr 3 and treated CsPb(Br 0.5 Cl 0.5 ) 3 has been fabricated, which achieves high detection stability, accuracy, and excellent repeatability compared to commercial UV radiometers. This work highlights a sustainable passivation approach and demonstrates the practical potential of natural antioxidants for perovskite‐based optoelectronic devices.