Improvement of Optical Characteristics of Organic Light-Emitting Devices by Nano-Scattering Films

Organic light-emitting devices (OLEDs) are very attractive due to their potential application in flat-panel displays and solid-state lighting. Especially, developing high power-efficiency devices to reduce energy consumption is one of the critical issues. Recently, the internal quantum efficiency (IQE) of electrophosphorescent organic light-emitting devices has approached nearly 100%. However, due to refractive-index mismatch between different material layers of OLEDs, light in OLEDs cannot be extracted effectively and suffers from total internal reflection. The out-coupling efficiency of conventional bottom-emitting devices is limited to about 20%. Here we demonstrate a method to enhance out-coupling of OLEDs. By integrating nano-scattering films　between the ITO electrode and the glass substrate, the external quantum efficiency of OLEDs can be enhanced by 1.96 times and the cd/A efficiency can be enhanced by 2.04 times compared to conventional bottom-emitting devices. The nano-scattering films can further decrease color shift over viewing angles, and the emission pattern becomes closer to the Lambertian distribution.