Narrow‐Linewidth Single‐Mode DFB Lasers Based on High‐Quality CsPbBr ₃ Quantum Dot Thin Films

Perovskite quantum dots (PQDs) are promising gain media for low‐threshold lasers, yet their integration into high‐quality distributed feedback (DFB) cavities has been severely limited by poor film compactness and morphological inhomogeneity. Here, we report a high‐performance CsPbBr 3 QD DFB laser enabled by a high‐concentration mixed‐solvent film‐formation strategy. Strongly binding 4‐dodecylbenzenesulfonic acid ligands allow the preparation of colloidally stable CsPbBr 3 QD inks with concentrations up to 200 mg mL −1 , providing sufficient optical gain. By introducing a binary solvent system composed of n‐hexane and n‐octane, the evaporation kinetics and fluid dynamics during spin coating are effectively regulated, yielding dense yet ultra‐smooth QD films. The optimized films exhibit strong waveguide–grating coupling, manifested by pronounced extinction resonances and a markedly enhanced Purcell effect upon integration with DFB gratings. As a result, efficient distributed feedback oscillation is achieved, leading to stable single‐mode surface‐emitting lasing with a linewidth as narrow as 0.23 nm, a low threshold of 29 µJ cm −2 , and a quality factor of approximately 2300. This work provides a versatile solution to overcome film‐quality‐induced cavity losses in CsPbBr 3 QD DFB lasers, and is expected to promote the development of high‐Q‐factor QD microcavity lasers.