Surface morphology control for low amplified spontaneous emission thresholds in quasi-2D lead-bromide perovskites

Quasi-two-dimensional (quasi-2D) lead halide perovskite materials have demonstrated remarkable potential as gain media for amplified spontaneous emission (ASE) and lasing. In recent years, significant progress has been obtained in reducing ASE thresholds and enhancing ASE stability for quasi-2D perovskites. The films with excellent surface morphology can effectively decrease the defect state density and suppress non-radiative recombination rates. However, achieving precise control over surface morphology remains challenging in minimizing optical losses for quasi-2D perovskite films. Here, we report a one-step solution-based approach to fabricate pinhole-free and ultra-smooth quasi-2D lead-bromide perovskite films by incorporating two types of short-chain organic cations, formamidinium (FA), and methylammonium (MA). The optimized perovskite film exhibits a roughness of ~1 nm and low scattering loss. Furthermore, improvements in crystal orientation enhance the crystalline quality of the samples. These merits promote ASE with an exceptionally low threshold of 4.0 μJ cm^-2 and a large exciton binding energy of 73.9 meV.