Room-Temperature Quasi-CW Random Lasing in a Tin-Perovskite Ultrathin Film

Solution-processed semiconductor laser diodes offer the prospect of low-cost and integrable coherent light sources. While lead (Pb)-based metal halide perovskites have shown significant progress in this field, their more environmentally benign tin (Sn)-based counterparts have lagged far behind, particularly in achieving continuous-wave (CW) operation, a critical step toward electrically pumped lasing. This is largely due to challenges in controlling crystallization and film morphology of Sn-based perovskites. Furthermore, conventional perovskite lasers typically require films several hundred nanometers thick to support well-defined guided modes and strong optical confinement, whereas the substantial thickness hinders efficient electrical injection. Here, we overcome these barriers by demonstrating quasi-CW random lasing in solution-processed CsSnBr₃ films as thin as ∼40 nm. By employing the additive N-benzylethylenediamine hydrogen bromide (BEABr), we retard the rapid crystallization of Sn-based perovskites, leading to a densely packed polygonal grain morphology. Multiple scattering at intrinsic grain boundaries provides coherent feedback, enabling random lasing under quasi-CW optical pumping with a threshold of 9.7 kW/cm² at room temperature. This work not only establishes the first quasi-CW lasing in a Sn-based perovskite but also presents a viable thin-film architecture that bridges optical and electrical design requirements, marking a critical advance toward solution-processed perovskite laser diodes.