Highly enhanced light extraction for organic light emitting diodes by self-assembly microlens-array films

Light extraction efficiency (LEE) and angular-spectrum stability of organic light emitting diode (OLED) are significantly improved by using self-assembly microlens-array films (MAFs) made of a monolayer based on silica microspheres and acrylic resin as light extractor. The close-packed light MAFs with a high fill factor of 71.42% was uniformly fabricated by a facile and low-cost solution process of spin-coating. The MAFs feature highly transmissive with transmittance of 86.2-90.6% and also high haze of 78.9-82.4% in UV-Vis regime. External quantum efficiency (EQE) of OLED with MAFs was significantly improved from 3.04 to 5.04%, corresponding to an enhancement of 66% compared with reference OLED. The small angular shift of CIE-indices is in a range of (0.008, 0.004), while viewing angle changes from 0 degrees to 60 degrees. Besides, the origin of high LEE and angular-spectrum stability was due to high scattering effect induced by high haze, leading to a Lambertian emissive profile. Notably, the proposed fabrication for the MAFs is simple and scalable, which was believed to be a promising approach for display and lighting applications.