Vapor Phase Growth of Centimeter‐Sized Band Gap Engineered Cesium Lead Halide Perovskite Single‐Crystal Thin Films with Color‐tunable Stimulated Emission

Abstract Single crystal metal halide perovskites thin films are considered to be a promising optical, optoelectronic materials with extraordinary performance due to their low defect densities. However, it is still difficult to achieve large‐scale perovskite single‐crystal thin films (SCTFs) with tunable bandgap by vapor‐phase deposition method. Herein, the synthesis of CsPbCl 3(1– x ) Br 3 x SCTFs with centimeter size (1 cm × 1 cm) via vapor‐phase deposition is reported. The Br composition of CsPbCl 3(1– x ) Br 3 x SCTFs can be gradually tuned from x = 0 to x = 1, leading the corresponding bandgap to change from 2.29 to 2.91 eV. Additionally, an low‐threshold (≈23.9 µJ cm −2 ) amplified spontaneous emission is achieved based on CsPbCl 3(1– x ) Br 3 x SCTFs at room temperature, and the wavelength is tuned from 432 to 547 nm by varying the Cl/Br ratio. Importantly, the high‐quality CsPbCl 3(1– x ) Br 3 x SCTFs are ideal optical gain medium with high gain up to 1369.8 ± 101.2 cm −1 . This study not only provides a versatile method to fabricate high quality CsPbCl 3(1– x ) Br 3 x SCTFs with different Cl/Br ratio, but also paves the way for further research of color‐tunable perovskite lasing.