Low‐Threshold Near‐Infrared Random Lasing Enabled by Phase Dimension Modulation in Quasi‐2D Tin‐Halide Perovskite Films

Quasi‐2D tin halide perovskites feature tunable photoluminescence from the visible to near‐infrared region, showing great potential for laser applications. However, studies on their lasing performance are mostly limited to low‐ n ( n ≤ 4) single crystals, while thin‐film counterparts remain largely underexplored. Here, we systematically characterize quasi‐2D tin halide perovskite thin films with n = 1–14 and reveal the correlation between n value and lasing behavior. A gas‐quenching strategy is developed to replace the conventional anti‐solvent method, regulating crystallization to form large grains and high‐n phases. Room‐temperature near‐infrared random lasing is successfully achieved in films with n ≥ 6. Optimized devices yield a low lasing threshold of 3.8 µJ cm −2 , a high quality factor over 1000, and excellent spectral reproducibility. The lasing threshold is among the leading performances reported for tin‐based perovskite random lasers operating under ambient conditions. The superior lasing performance in high‐ n films originates from improved crystallinity, favorable orientation, suppressed exciton‐phonon coupling, and reduced non‐radiative recombination. This work confirms quasi‐2D tin halide perovskites as promising gain media for near‐infrared lasers and offers an effective approach for high‐performance lead‐free optoelectronic devices.