Picosecond low-threshold random lasing in polymer passivated CsPbBr₃ thin films

All-inorganic CsPbX₃ (X = Cl, Br, I) perovskites have demonstrated great potential for optoelectronic applications due to their excellent optical properties and environmental stability. Random lasing is a particularly promising direction because of its simple and cavity-free feedback mechanism. However, efficient random lasing in CsPbX₃ thin films remains challenging because of their high defect densities, non-radiative recombination rate, and poor surface morphology. Herein, we present a simple method to fabricate high-quality CsPbBr₃ thin films, using polymethyl methacrylate–toluene solution as antisolvent, which simultaneously enables surface passivation of perovskite crystals. The as-synthesized films exhibit improved crystallinity, smoother morphology, and prolonged carrier lifetime. Owing to these factors, the films achieve a low threshold random lasing (9.59 µJ/cm²), along with an ultrafast photon decay of 3.14 ps at 2.4 times the threshold. Notably, the random lasing can be realized across the sample area. This work highlights the effect of polymer passivation in enhancing film quality and enabling low-threshold, short-pulse random lasing. These findings provide a promising strategy for large-area, multi-point integrated photonics applications based on perovskite thin films.