Amplified Spontaneous Emission with a Low Threshold from Quasi‐2D Perovskite Films via Phase Engineering and Surface Passivation

Abstract Solution‐processed quasi‐2D Ruddlesden‐Popper perovskites are being considered as a promising optical gain medium in lasing applications, owing to their outstanding optoelectronic properties and inherent stability. However, the development of quasi‐2D perovskites for lasers with low threshold and high optical gain is still lagging far behind 3D‐perovskites. This work proposes an anti‐solvent treatment strategy to regulate the phase components and surface morphology of quasi‐2D PEA₂(CsPbBr₃)_n−1PbBr₄ thin films. Furthermore, an additional poly(methyl methacrylate) coating is introduced to reduce the surface defects of perovskite films and suppress the non‐radiative recombination. Due to the phase engineering and surface passivation, excellent amplified spontaneous emission (ASE) is obtained with a low threshold of 11.7 µJ cm⁻² and a high net model gain of 622 cm⁻¹. In addition, under 800 nm femtosecond laser excitation, two‐photon‐pumped ASE is also successfully observed with a low threshold of 7.2 mJ cm⁻².