Stable and Low‐Threshold Amplified Spontaneous Emission in Quasi‐2D Perovskite Films with Mixed Ruddlesden–Popper and Dion–Jacobson Phase

Dion–Jacobson (DJ) phase halide perovskites have garnered significant attention in photoluminescence applications due to their excellent stability compared to three‐dimensional (3D) perovskites. However, in solution‐processed DJ‐phase perovskite films, the complex crystallization process and the formation of multi‐dispersed quantum well structures significantly impact the optoelectronic properties of the DJ‐phase perovskite. This work presents a quasi‐two‐dimensional (quasi‐2D) mixed‐phase perovskite (MPP) film by introducing Ruddlesden–Popper (RP)‐type aromatic ammonium cations into the DJ‐phase precursor. The resulting MPP 0.2 film, with the chemical formula (PEA 2 ) 0.2 HDA 0.8 FA 7 Pb 8 Br 25 (where HDA = hexamethylenediammonium and PEA = phenylethylammonium), exhibits improved morphology, a more uniform distribution of n phase components, higher crystallinity, and enhanced hydrophobicity compared to the neat DJ‐phase films. Notably, the amplified spontaneous emission (ASE) threshold of the quasi‐2D MPP 0.2 film decreased from 120 to 60 μJ/cm 2 . This research shows that quasi‐2D MPP films have great potential as waveguide materials for stable, low‐threshold ASE.