Mixing Dion–Jacobson and Ruddlesden–Popper Structures in Quasi‐2D Perovskite Films for Thermal‐ and Photo‐Stable Stimulated Emission

Abstract Quasi‐two–dimensional (2D) perovskite films are promising candidates as a gain medium for stimulated emission owing to their hydrophobicity and efficient energy funneling that facilitates the population inversion. However, the commonly used Ruddlesden–Popper (R–P) perovskites still suffer from instability induced by high‐density pumping as well as the resulting heating effect. Here, quasi‐2D perovskite films with mixed Dion–Jacobson (D–J) and R–P phases are demonstrated with both excellent amplified spontaneous emission (ASE) properties and thermal‐ and photo‐stabilities under ambient conditions. In these films, octyl ammonium bulky organic cations are used to obtain the preferred crystal orientation and highly smooth surface for low‐threshold ASE, while 1,8‐octanedi ammonium cations contribute to the greatly improved stability. The films containing the D–J phase exhibit good structural stability even after 130 °C heat treatment for 48 h. The mixed‐ligands film maintains a low ASE threshold of 11.6 µJ cm⁻² and a high optical gain of 413 cm⁻¹ after environmental annealing. It is demonstrated that it is the diammonium that firmly bonds to the perovskite layer,allowing the maintenance of quasi‐2D perovskite structure and good ASE performances.