Enhanced Photostability of the Colloidal Ruddlesden–Popper Perovskite Nanoplate through 4-Fluorobenzylammonium Iodide-Mediated Surface Engineering for Photoluminescent Application

UV light-induced photodegradation of the organic–inorganic hybrid (OIH) Ruddlesden–Popper (RP) perovskite nanoplates (NPls) is a crucial bottleneck for optoelectronic application in the future. Continuous UV exposure triggers the deprotonation of the spacer as well as the A-site cation (CH 3 NH 3 + ), ultimately leading to lattice collapse. To combat this photoinstability, we introduce a surface modification of colloidal OIH RP NPls, (OAm) 2 (CH 3 NH 3 PbI 3 ) 2 PbI 4 ( n = 3) (OAm stands for oleylammonium cation) by 4-fluorobenzylammonium iodide (4FBAI). In ambient conditions, conventional NPls deteriorate within 80 min of UV exposure, whereas the 4FBAI-modified NPls exhibit remarkable endurance, maintaining structural integrity for 12 h with only a 11% reduction in the initial photoluminescence (PL). Interestingly, benzylammonium iodide (BAI) and 4-methoxybenzylammonium iodide (4OBAI)-treated NPl fail to provide similar photostability, thus signifying the importance of the fluorine atom. The fluorine atom enhances the positive charge density of the ammonium ion and facilitates faster deprotonation compared to parental ammonium ions (here, OAm + and CH 3 NH 3 + ) under UV exposure. This ensures the survival of the parent nanoplate structure. Along with the photostability enhancement, the PL quantum yield of the treated NPl also increases to 50 ± 2 from 35 ± 2%. This research not only addresses the pressing photostability issue of RP NPl stability but also illuminates the pivotal role of specific chemical modifications, such as fluorine atom incorporation, for the fabrication of UV-stable perovskite devices in the future.