Ultra-Efficient Optical Gain and Lasing in MDACl₂-Doped Perovskite Thin Films

Solution-processed perovskite materials have been enticing candidates for optical gain and lasing media because of their low cost, remarkable color purity, facile bandgap tunability, and high absorption cross-section. However, it is difficult, if not impossible, for them to highly amplify light with stable operations because they experience severe non-radiative emission losses due to their high density of surface and bulk defect centers and irregular composition. Here, we report that incorporating 5% of methylenediammonium dichloride (MDACl₂) into mixed perovskite systems leads to a drastic reduction in the density of iodide interstitials and surface recombination losses. Subsequently, we record that MDA-treated, cavity-free thin perovskite films exhibit very photostable and ultra-low threshold amplified spontaneous emission of <6 μJ/cm², approximately 30 times lower than the untreated films. Moreover, an ultra-high optical gain of 1000 cm^-1is successfully achieved, representing the highest reported gain for cavity-free perovskite films. These results are fully supported by extensive high-level density functional theory calculations and ultrafast transient absorption measurements. These findings will serve as a benchmark for the design and fabrication of low-threshold, high amplification perovskite media for lasers and light emission applications.