Accelerating the Hot Carrier Cooling for Phonon Management of Quasi‐2D Perovskite Films Toward Low‐Threshold Lasing

Abstract Hot‐phonon bottleneck effect seriously restrains hot carrier cooling, which significantly affects the performance of optoelectronic devices. Manipulating fast hot carrier cooling is both fundamental and crucial for accelerating carrier accumulation at the band edge, thereby facilitating population inversion. Here the phonon landscape is restructured by altering the local chemical environment of the lead‐halide framework using molecular engineering in quasi‐2D perovskites via crown ether (18‐crown‐6). Density functional theory (DFT) calculations and Raman spectroscopy confirm a pronounced amplification of the Pb─Br derived longitudinal optical (LO) phonon mode in the 18‐crown‐6 decorated quasi‐2D perovskite film. Transient absorption spectroscopy (TAS) further reveals the rapid hot carrier cooling with a mitigated hot‐phonon bottleneck facilitated by the efficient electron‐LO coupling. Such phonon modulation results in an ultralow amplified spontaneous emission (ASE) threshold of 0.8 µJ cm −2 , which represents a 2.5‐fold threshold reduction compared with the pristine film. Furthermore, single‐mode lasing is successfully demonstrated with a low threshold of 2.2 µJ cm −2 , among the lowest values in quasi‐2D perovskites‐based lasers. These findings underscore the potential of phonon management as a scalable and tunable strategy for developing perovskite photonic platforms.