Biuret-Engineered Mixed-Cation Perovskite with High Optical Gain for Single-Mode VCSELs

Abstract Metal halide perovskites are attractive gain media for coherent lasers due to their high optical gain, strong photoluminescence and tunable bandgap. Mixed-cation design can optimize lattice structures and mitigate nonradiative recombination, but mismatched crystallization and incomplete precursor conversion may introduce grain defects and metallic Pb0 species. Pb0-related deep traps exacerbate carrier losses and deteriorate overall lasing performance. This work presents a bifunctional modification strategy using biuret to suppress Pb0 precipitation and passivate defects in mixed-cation perovskites. Owing to carbonyl and amino groups, biuret simultaneously restrains Pb0 formation via Lewis acid–base coordination and passivates defects through hydrogen bonding with bromide ions. The modified perovskite films possess a material gain of 3754 cm–1, an extended gain lifetime of 148 ps, a low amplified spontaneous emission (ASE) threshold of 2.60 μJ cm–2, and improved long-term ASE stability. The constructed single-mode vertical-cavity surface-emitting laser (VCSEL) delivers outstanding lasing performance with a narrow emission line width of 0.068 nm and a high Q factor of 7848. This study reveals the relationship between Pb0 inhibition, defect passivation and optical gain, and offers a practical route for high-performance perovskite lasers.