HighlightsSynergistic effect triggers the Ostwald ripening for the downward recrystallization of perovskite to form buried submicrocavities as light output coupler.The simulation suggests the buried submicrocavities can improve the light out-coupling efficiency from 26.8% to 36.2% for near-infrared light.Light-emitting diodes yields peak external quantum efficiency increasing from 17.3% at current density of 114 mA cm−2to 25.5% at current density of 109 mA cm−2and a radiance increasing from 109 to 487 W sr−1m−2with low rolling-off.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40820-023-01097-3.