One-Step Co-Evaporation of All-Inorganic Perovskite Thin Films with Room-Temperature Ultralow Amplified Spontaneous Emission Threshold and Air Stability.

Inorganic cesium lead halide perovskite has been successfully applied in the optoelectronic field due to its remarkable optical gain properties. Unfortunately, conventional solution-processed CsPbX3 films suffer unavoidable pinhole defects and poor surface morphology, severely limiting their performance on amplified spontaneous emission (ASE) and lasing applications. Herein, a dual-source thermal evaporation approach is explored to achieve a uniform and high-coverage CsPbX3 polycrystalline thin film. It was found that one-step co-evaporated CsPbBr3 (OC-CsPbBr3) thin films without post-annealing exhibit an ultralow ASE threshold of ∼3.3 μJ/cm2 and a gain coefficient above 300 cm-1. The coexistence of cubic and orthorhombic phases in these materials naturally form an energy cascade for the exciton transfer process, which enables rapid accumulation of excitons. Stable ASE intensity without degradation for at least 7 h is also realized from OC-CsPbBr3 thin films under continuous excitation, which is superior to that in the solution-processed CsPbBr3 thin films. Notably, a Fabry-Pérot cavity laser based on the OC-CsPbBr3 thin film is first achieved, featuring an ultralow lasing threshold (1.7 μJ/cm2) and directional output (a beam divergence of ∼3.8°). This work highlights the noteworthy optical properties of OC-CsPbBr3 thin films, leading to potential available applications in integrated optoelectronic chips.