Ligand Assisted Epitaxial Growth of CsPbBr 3 Microcrystal Resonators With Record ‐Low Lasing Thresholds

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We introduce ligand‐assisted epitaxial growth (LAEG) for lead‐halide perovskites, enabling the formation of high‐quality, single‐crystalline epitaxial microstructures. In this approach, ligands fulfill multiple critical functions: they regulate crystal growth by slowing crystallization kinetics, allowing the formation of epitaxial microcrystals with smooth surfaces and well‐defined morphologies; they protect the perovskite from environmental degradation; and they passivate surface states. Near‐ambient‐pressure X‐ray photoelectron spectroscopy confirms well‐preserved surface stoichiometry of CsPbBr 3 enabled by ligand protection. The LAEG method is broadly applicable to different ligands, perovskite compositions, and substrates, consistently yielding higher material quality than non‐ligand‐assisted solution epitaxy. CsPbBr 3 epitaxial microcrystals exhibit a high photoluminescence quantum yield of ∼50% and nearly temperature‐independent photoluminescence decay dynamics up to 80°C, demonstrating strong thermal robustness relevant for optoelectronic devices. Lasing is observed up to 90°C, and improved thermal management enhances operational lifetime. Micro‐resonator lasers grown on mica substrates exhibit record‐low threshold excitation powers among microcrystal‐based perovskite lasers, outperforming previously reported CsPbBr 3 devices and those grown on PbS substrates due to favorable refractive‐index contrast enabling total internal reflection. Overall, LAEG provides a simple yet powerful route to high‐quality perovskite epitaxy and is expected to be extendable to lower‐dimensional perovskite systems with enhanced and tunable optical properties.