Phase Distribution Control in Thermally Evaporated Perovskite Films for Speckle-Free Laser Imaging
Metal-halide perovskites exhibit exceptional optical gain, narrow emission linewidths, and high emission efficiency, positioning them as promising candidates for next-generation lasers. Thermal evaporation, a mature semiconductor fabrication technique, offers scalability, yet monitoring phase distribution during deposition remains challenging. This study systematically investigates and regulates thermally evaporated FAxCs0.8PbBr3 perovskite films by tuning formamidinium (FA) content to optimize phase distribution. At intermediate FA content, films achieve a balanced distribution of n=2 to n=5 quantum-well phases, facilitating ultrafast carrier transfer (<0.31 ps) and suppressing nonradiative recombination. FA+ actively incorporates as an A-site cation, promoting ordered crystallization and reducing defect densities. The optimized films exhibit a net modal gain of 1041 cm−1 and a gain lifetime of 129 ps. Benefiting from efficient internal scattering, the threshold for cavity-free random lasing is reduced to below 5 μJ/cm2 at room temperature. The low spatial coherence of random lasing enables 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, advancing speckle-free laser imaging systems compatible with semiconductor-grade, large-area manufacturing.