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 SnO2 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.

1. Introduction

Due to their outstanding physical properties, all-inorganic lead halide perovskites with the chemical formula CsPbX3 have attracted significant attention for optoelectronic applications, such as solar cells [1–7], light-emitting diodes (LEDs) [8–10], photodetectors (PDs) [11–20], lasers, and imaging [21, 22]. Among these, PDs, which convert light into electrical signals, are essential for optical communication, biomedicine, space exploration, and imaging [23]. Nevertheless, due to the chemical instability of perovskites under moisture, light, and heat exposure, solution-processed perovskite-based PDs have not achieved the widespread adoption initially predicted by the industry [24, 25]. One primary source of instability stems from the presence of numerous defects in perovskite lattices, including uncoordinated Pb2+, halogen vacancies (VX), and Pb-I antisites (PbI3−), which act as non-radiative recombination centers and ionic migration pathways, ultimately degrading device performance [2–4, 14, 26].

Leveraging Lewis acid–base interactions and hydrogen bonding, incorporating Lewis base-functionalized electron-donating organic molecules (e.g., –CN, –NH2, –Cl, –C=O) into perovskite films remains an effective and widely used approach for trap-state passivation [1–4, 24, 27–30]. These functional groups can donate lone pair electrons to undercoordinated positive charge centers, such as Lewis acidic Pb2+, forming coordinate bonds and reducing trap states. Notably, bifunctional Lewis base/proton-donor molecules (e.g., –OH, –NH2) exhibit strong passivation via coordinating undercoordinated Pb2+, forming H-bonds with I−, and passivating the other cationic and anionic defects. Furthermore, when engineered into a conjugated molecular framework, particularly aromatic systems, this dual functionality significantly amplifies passivation effectiveness through synergistic π-π conjugation between carbon–carbon double bonds (–C=C) and p-π conjugation linking –C=C to carbonyl (–C=O) or imine (–C=N) groups. Additionally, incorporating extended conjugated system molecular structures can also further enhance the stability of the passivator. However, the encapsulated devices remain susceptible to prolonged UV exposure, which leads to perovskite decomposition and performance degradation [31–36]. Consequently, significant efforts focus on the strategi