Top Emitting OLEDs with multi-layered Mirror Consisting of Metallic and Dielectric Layers

We report on an investigation into the design and optimization of multi-layered mirror structures for top-emitting organic light emitting diodes (OLED). Our results show that the six-layer top mirror structure with optimally designed dielectric-enhanced metallic capping mirror proposed here exhibits more than three-fold improvement in the device luminance over the conventional LiF/Al top mirror The optical and electrical simulations were performed on a set of microcavity OLEDs consisting of widely used organic materials, N,N´-di(naphthalene-1-yl)-N,N´-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq₃) as emitting and electron transporting layer. Ag was used as the anode/bottom mirror for maximum reflection. In order to optimize both the injection characteristics of the cathode and the cavity effect the structure of the multilayer top mirror was optimized, the structure used was a combination of a thin LiF/Al cathode capped by metallic and dielectric layers. The electroluminescence emission spectra, electric field distribution inside the device, carrier density, recombination rate and exciton density were calculated for devices with different top mirror configurations.