High Optical Gain in Stable MOF‐Derived Composite Films Based on Perovskite Nanocrystals

Metal halide perovskite nanocrystals hold great promise for low‐cost optoelectronic and lasing applications, yet their integration into composite films is limited by poor stability under high excitation. We present a strategy to fabricate stable, ligand‐free perovskite nanocrystal‐based composites by combining lead‐based metal‐organic frameworks (MOFs) with methylammonium acetate ionic liquid. This single‐step fabrication approach conducted in air yields compact, smooth (∼3 nm roughness), optically uniform composite films with a high perovskite incorporation level. These films exhibit broad spectral tunability over the 409–752 nm range, high photoluminescence quantum yields of up to 80%, and exceptional stability, maintaining > 80% emission intensity for over 190 h under elevated temperature and ultraviolet irradiation in air. Moreover, owing to efficient confinement and suppressed nonradiative losses, optimized composite films deliver a record modal gain of 1825 cm −1 at 350 µJ∙cm −2 , which is among the highest values reported for perovskite nanocrystals. Our findings establish MOF‐derived perovskite nanocrystal composites as a scalable platform for high‐performance optoelectronics, paving the way toward practical perovskite‐based lasers.