Optical Enhancement in Optoelectronic Devices using Refractive Index Grading Layers.

We enhanced the optical transmittance of multilayer barrier film by inserting refractive index grading layer (RIGL). The result indicates that the Fresnel reflection, induced by the difference of refractive indices between SixNy and SiO2, is reduced by the RIGL. To eliminate the Fresnel reflection while maintaining high transmittance, the optimized design of grading structures with the RIGL was conducted using an optical simulator. With the RIGL, we achieved averaged transmittance in the visible wavelength region by 89.6 %. It is found that the optimized grading structure inserting the multilayer barrier film has a higher optical transmittance (89.6%) in the visible region than that of a no grading sample (82.6%). Furthermore, luminance is enhanced by 14.5 % (from 10190 to 11670 cd m-2 at 30 mA cm-2) when grading structure is applied to OLEDs. Finally, the results offer new opportunities in development of multilayer barrier films, which assist industrialization of very cost effective flexible organic electronic devices.