The light out-coupling efficiency of OLEDs is enhanced by the use of a refractive index modulation layer (RIML) with MgO nanofacet structure (see figure) that can be formed without an additional lithographic or patterning processes. Increases in luminance and power efficiency of up to 19% and 34.7%, respectively, are demonstrated. Low out-coupling efficiency is one of the main limitations to highly efficient OLEDs, so overcoming it would allow substantial improvements.