A simple and efficient method to fabricate light extraction layers is demonstrated by utilizing the phase separation of two polymer blends to enhance the light out-coupling efficiency of OLEDs with low haze. Polystyrene and poly(methyl methacrylate) dissolved in tetrahydrofuran are mixed and spin-coated over ITO-coated glass substrates. Nanopores and nanopillar arrays are formed through lateral phase separation of the polymer blend. The shape, size, and distribution of the patterns can be controlled through changes in the composition and thickness of the coated polymer blends. Phosphorescent OLEDs are fabricated using randomly dispersed nanopillar arrays as light extraction layers and they show a 24% enhancement in external quantum efficiency with a Lambertian emission pattern, no spectrum dependence on viewing angles, and only a small increment in the haze. With these advantages, this newly developed method can be adapted to be used for large-area, flexible substrates for lighting and display applications.