Enhancing Ultraviolet Stability and Operational Durability of Perovskite Photodetectors by Incorporating Chlorine into Thermally-Switchable Tautomeric Passivators

Abstract UV-absorbing additives have recently been demonstrated to be effective interfacial modifiers that simultaneously enhance the UV stability and crystallization of halide perovskite. However, the underlying mechanisms concerning UV absorption, defect passivation, and efficacy optimization of these additives remain unresolved. Herein, two UV tautomeric absorbers (UV320 and UV327) are selected as defect-passivators for perovskites. The keto–enol tautomeric evolution processes and corresponding defect passivation performance/mechanism of both the original molecules and their tautomers are thoroughly compared and elucidated through experimental characterizations and density functional theory calculations. The additional carbonyl (–C=O) groups generated through the keto–enol tautomeric process triggered by the Cl atom in UV327 ultimately provide superior chemical coordination and enhanced defect-passivation capability compared to the original counterparts. Moreover, the versatility of K-UV327 is further demonstrated by its optimization of SnO 2 film quality, interfacial energy band alignment, charge extraction efficiency, and defect state suppression. The photodetector optimized by UV327’s tautomer achieves an ultralow dark current density of 3.22 × 10 −10 A cm −2 , an enhanced linear dynamic range of 94.14 dB, and a fast response time of 23.35/26.19 μs. Notably, unencapsulated devices maintain a stable response at 3900 Hz following 300 h exposure to 40% ± 5% relative humidity and 30 h UV irradiation.