Narrow‐Linewidth Continuous‐Wave Perovskite Nanolasers via Conformal DFB Gratings

Integrating solution‐processed perovskite gain media into silicon photonic platforms is challenging because of the competition between precursor infiltration and crystallization. Here, by tuning the solvent extraction rate via controlled antisolvent volume, we synchronize the precursor infiltration and crystallization kinetics on DFB gratings, enabling complete trench filling and uniform conformal growth with few structural defects. This structural continuity supports stable Bragg feedback, yielding wavelength‐tunable lasing (543–554 nm, 2 nm step). Under pulsed pumping, the laser has a linewidth of 0.15 nm and a threshold of 15.8 µJ cm − 2 (Q ≈ 3600). Room‐temperature continuous‐wave lasing is also demonstrated with a threshold of 15 W cm − 2 (Q ≈ 1700). This solvent‐extraction‐controlled crystallization strategy provides a general path to determining the morphology of solution‐processed semiconductors directly on nanostructured substrates for on‐chip coherent light sources.