Low‐Threshold, External‐Cavity‐Free Flexible Perovskite Lasers

Abstract A distinct advantage of halide perovskite semiconductors is their potential as gain media in high‐performance, all‐solution‐processed flexible lasers. However, most perovskite microlasers employ external optical resonators with rigid and high‐temperature/vaccum‐processed structures unsuitable for flexible applications. Here, low‐threshold, external‐cavity‐free perovskite lasers (≈550 nm, linewidth: ≈0.3 nm, quality factor: ≈1900, room temperature), prepared with excellent reproducibility using simple one‐step spin‐coating and low‐temperature annealing, are demonstrated. Exceptionally low lasing thresholds of 9.3 and 14.6 µJ cm −2 are achieved for external‐cavity‐free perovskite lasers on rigid and flexible substrates, respectively. The thresholds and quality factors are on par with that of high‐performance perovskite microlasers with well‐designed external cavities. The lasers exhibit good operational stability, showing half‐life of >1.8 × 10 8 pulses under optical pumping in air. Transient optical experiments reveal that the low thresholds stem from enhanced band‐to‐band spontaneous and stimulated emission processes in the high‐quality microcrystalline perovskite, effectively out‐pacing trap‐mediated and Auger processes detrimental to the lasing action. The flexible perovskite lasers retain >95% of the initial intensity after 10000 bending cycles, showing outstanding mechanical durability. As these lasers can be produced from solution within minutes at low costs, the findings are expected to enable high‐throughput, scalable fabrication of perovskite lasers for emerging applications.