Red Low-threshold Amplified Spontaneous Emission of Perovskite Films Achieved by A-site Substitution and Defect Passivation

Lead halide perovskite has shown great potential as a new generation of optoelectronic materials due to its adjustable optical band gap，high luminous color purity，high carrier mobility，and solution-processibility. Currently，amplified spontaneous emission（ASE）and laser have been realized in the blue，green，red，and even infrared ranges for perovskite material. As a red light-emitting optical gain medium，CsPbI2Br perovskite material has good thermal stability and a suitable optical band gap and has attracted extensive attention from researchers. However，CsPbI2Br films prepared by the solution method are prone to phase transition in high-humidity environments，and there are many defects in the films，which hinder their further development. To improve the phase stability of CsPbI2Br perovskite films，the A-site is partially substituted by FA+（CH4N2+） in this work. The tolerance factor of the perovskite structure is increased after FA+ substitution，which can effectively improve the phase stability of the perovskite films. Meanwhile，the morphology and crystallinity of the perovskite films are improved. To reduce the non-radiative recombination caused by the surface defects，polymethyl methacrylate（PMMA）is used to passivate the surface of the perovskite films. The C==O bond in PMMA can effectively bind to the undercoordinated Pb2+ on the surface of perovskite，resulting in a good defect passivation effect and effective inhibition of non-radiative recombination. Thanks to the improvement of the film morphology caused by FA+ cation and the PMMA passivation，a low-threshold，15 μJ/cm2 under nanosecond laser excitation is achieved for the red ASE of the Cs0. 7FA0. 3PbI2Br perovskite film. At the same time，the film has good hydrophobicity and photostability. Under the air humidity environment（RH（40 ± 10）%），the ASE intensity remains at 93% of its initial value after a pulsed laser irradiation of 3 000 μJ/cm2 for 120 min. This work provides a reference for realizing low-threshold and high-stability red ASE and laser. © 2024 Editorial Office of Chinese Optics. All rights reserved.