Light-induced photoluminescence enhancement in MAPbBr3 thin films: PMMA-mediated divergence in kinetics and spectral evolution

Photoluminescence (PL) enhancement in lead halide perovskites under continuous illumination is commonly attributed to light-induced ion migration and defect healing. Here, we report a significant light-induced PL enhancement in methylammonium lead bromide (MAPbBr 3 ) perovskite thin films, achieved through a simple one-step spin-coating nanocrystal-pinning method. A comparative study of unencapsulated (Pristine) films and films embedded in a poly(methyl methacrylate) matrix (Pvsk@PMMA) under continuous UV irradiation (273 nm) reveals pronounced PL enhancement in both, but with starkly different kinetics and spectral evolution. The Pristine film shows a gradual, sustained increase of ≈ 2352% in PL intensity over 120 min, accompanied by a red-shift and a 42.8% reduction in emission linewidth. In contrast, the Pvsk@PMMA film exhibits a rapid ≈ 123% enhancement that saturates within 15 min, along with a slight blue-shift and a 15.8% linewidth broadening. Based on the combined spectral, kinetic, and structural characterization, we propose that light-driven ion migration and Frenkel-pair annihilation are responsible for defect healing in both cases. Crucially, the PMMA matrix plays a dual role: it passivates surface traps and suppresses grain agglomeration, while interfacial interactions contribute to the observed distinct spectral blue-shift and kinetic saturation. Remarkably, the Pvsk@PMMA film retained 97.91% of its initial PL intensity after 18 months of ambient storage, demonstrating the protective role of the PMMA matrix. This study demonstrates a straightforward pathway for tailoring the intensity and spectral properties of green emission from MAPbBr 3 thin films for next-generation optoelectronic devices.