Break-through amplified spontaneous emission with ultra-low threshold in perovskite via synergetic moisture and BHT dual strategies

Micro-nano lasers hold significant promise for on-chip integrated photonics, where perovskite materials emerge as compelling gain media despite stability challenges. While moisture typically degrades perovskite structures, its controlled integration can paradoxically enhance crystallization. Here, we demonstrate a synergistic strategy utilizing water molecules and butylated hydroxytoluene (BHT) additive to achieve high-quality methylammonium lead iodide (MAPbI₃) films with low defect density. Through optimized BHT (4 wt%) combined with 95% relative humidity treatment, we attain an unprecedented amplified spontaneous emission (ASE) threshold of 8.987 μJ cm⁻² under nanosecond pulse excitation - the lowest value reported to date. This dual-triggered film completes ASE intensity retention after 30-day ambient storage. In situ structural and optoelectronic characterization reveals that BHT extends water-perovskite interaction, facilitating organic cation vertical diffusion and preferential (110)-oriented crystallization with 53.02% perpendicular alignment. Transient absorption (TA) spectroscopy confirms suppressed non-radiative recombination, evidenced by 11% prolonged carrier lifetime (6145 ps), while temperature-dependent photoluminescence reveals enhanced exciton binding energy (73.50 meV vs. 60.68 meV) conducive to low-threshold lasing. This work transforms moisture from a degradation agent into a crystallization promoter, establishing a paradigm for high-performance perovskite lasers with simultaneous efficiency and stability.