Phase distribution control in thermally evaporated perovskite films for speckle-free laser imagingPhase distribution control in thermally evaporated perovskite films for speckle-free laser imaging

Metal-halide perovskites possess excellent optical gain, narrow emission linewidths, and high emission efficiency, rendering them highly promising for next-generation laser applications. Thermal evaporation, a mature semiconductor fabrication technique, offers a viable route toward scalable production. However, to monitor the phase distribution of perovskites in thermally evaporated process is still challenging. Here, we systematically investigated and regulated thermally evaporated FAXCs0.8PbBr3 perovskite films by tuning the FA content to optimize the phase distribution. At an intermediate FA content, the film exhibited a more balanced distribution of n = 2 to n = 5 quantum-well phases, which facilitated ultrafast carrier transfer (<0.31 ps) and suppressed nonradiative recombination. FA+ actively participates in the perovskite lattice as an A-site cation, contributing to more ordered crystallization and lower defect densities. The optimized film achieved a net modal gain of 1041 cm-1 and a gain lifetime as long as 129 ps. Furthermore, benefiting from the efficient internal scattering, the threshold for cavity-free random lasing is successfully effectively reduced to below 5 μJ/cm² at room temperature. The low spatial coherence of the random lasing enabled speckle-free imaging with a speckle contrast as low as 0.011 and improved contrast-to-noise ratios across all spatial frequencies. This work provides a scalable strategy for perovskite composition-phase engineering, paving the way toward speckle-free laser imaging systems compatible with semiconductor-grade, large-area manufacturing techniques.