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

ABSTRACT 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.