摘要： Inorganic cesium lead halide perovskite has been successfully applied in 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 application. Herein, a dual-source thermal evaporation approach is explored in our work to achieve a uniform and high-coverage CsPbX3 polycrystalline thin film. It is found that the one-step co-evaporated CsPbBr3 (OC-CsPbBr3) thin films without post-annealing exhibit an ultralow ASE threshold of ~ 3.3 μJ/cm2 and gain coefficient above 300 cm-1. The coexistence of cubic and orthorhombic phases in this 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 hours is also realized from OC-CsPbBr3 thin films under continuous excitation, which is superior to that in the solution-processed CsPbBr3 thin film. Notably, a Fabry-Perot (F-P) cavity laser based on the OC-CsPbBr3 thin film is first achieved, featuring an ultralow lasing threshold (1.7 μJ/cm2) and directional output (beam divergence of ~ 3.8°). This work highlights the noteworthy optical properties of OC-CsPbBr3 thin films, leading to potential available applications in the integrated optoelectronic chips.