Stable, Room-Temperature, Low-Threshold Amplified Spontaneous Emission from Thermally Evaporated Cesium Lead Halide Perovskites

Semiconductor nanocrystals are widely investigated as tunable quantum emitters due to their composition-, size- and shape-dependent optical properties, and they find applications in various optoelectronic devices, including lasers. However, in compact films, insulating ligands often limit heat and charge transport. Improving the heat management, for example, by removing ligands, can significantly enhance the operational stability at high excitation densities required for laser devices. Here, we report the synthesis, structural characterization, and stable high optical gain of ligand-free nanocrystalline thin films obtained through single-source thermal evaporation of CsPbX₃ (X = Cl, Br). This deposition method is robust, scalable, and compatible with industrial processes. A slow postdeposition crystallization process under nitrogen yields compact, smooth, and optically uniform thin films with nanocrystalline grains with weakly confined optical features and pronounced excitonic resonances. The films show composition-tunable (430-545 nm), low-threshold (<i>ca</i>. 2 μJ cm^-2) amplified spontaneous emission, with a high net modal gain of 890 cm^-1 measured for the pure CsPbBr₃ composition. Due to the enhanced heat dissipation enabled by the optimized film morphology, the operation stability under ambient conditions surpasses 180 million laser shots (<i>i</i>.<i>e</i>., 5 h of continuous operation), with merely ∼8% degradation, indicating that thermally evaporated perovskite thin films are promising optical gain media for room-temperature lasing applications.