Solving the Oled Outcoupling Problem Using Aperiodic Dielectric Stacks
Peter Peumans, Electrical Engineering, Stanford University, 330 Serra Mall, Stanford, CA 94305
Standard OLED structures waste up to 80% of the emitted photons due to emission into total internal reflection modes in the substrate, dielectric waveguide modes and surface plasmons. Several approaches to improve the outcoupling efficiency have been proposed, such as the use of substrate scattering and microlenses, and microcavities using distributed bragg reflectors. Each of these schemes has its shortcomings, such as pixel blurring, non-Lambertian emission, CIE coordinate shift with angle, etc. We will report on an outcoupling scheme that has none of these disadvantages. It is based on precise control over the phase and reflection of light from a dielectric stack interposed between the substrate and transparent electrode. Such photonic structures allow us enhance the outcoupling efficiency while maintaining Lambertian emission over a specified angular range. I will discuss theory and experiment and discuss the limits of this approach.