Unraveling the Ultrafast Carrier Dynamics and Lasing Pathways in 2D Tin Halide Perovskites

Abstract Tin‐based 2D metal halide perovskites have emerged as promising solution‐processable semiconductors with superior optoelectronic properties, high tunability, and non‐toxicity. Notably, they exhibit efficient and stable lasing with reduced thresholds compared to their lead‐based analogues. However, despite significant progress in lasing performance through material design and ligand engineering, the fundamental photophysical origins of stimulated emission in these materials remain underexplored and are far less understood than those in Pb‐based perovskites. In this work, lasing behavior and exciton dynamics in the prototypical tin‐based 2D perovskite (PEA) 2 SnI 4 are investigated using ultrafast optical spectroscopy (PEA + = phenylethylamine cation). Fluence‐dependent transient reflectance (TR) and photoluminescence measurements reveal that the material can sustain high exciton populations and support stimulated emission from biexcitons. Early‐time dynamics show exciton accumulation and screening effects at high fluences, while spectral‐temporal photoluminescence data indicate that well above threshold, lasing is accompanied by mode broadening and redshift due to excess thermalized excitons, and excessive excitation density destabilizes stimulated emission. The mechanistic understanding from this work will help to guide the design of more robust Sn‐based 2D perovskites for lasing applications.