Optimization of microcavity OLED by varying the thickness of multi-layered mirror

Abstract

We optimized the emission efficiency from a microcavity OLEDs consisting of widely used organic materials, N,N′-di(naphthalene-l-yl)-N,N′- diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq 3) as emitting and electron transporting layer. LiF/Al was considered as a cathode, while metallic Ag anode was used. TiO 2 and Al 2O 3 layers were stacked on top of the cathode to alter the properties of the top mirror. The electroluminescence emission spectra, electric field distribution inside the device, carrier density, recombination rate and exciton density were calculated as a function of the position of the emission layer. The results show that for certain TiO 2 and Al 2O 3 layer thicknesses, light output is enhanced as a result of the increase in both the reflectance and transmittance of the top mirror. Once the optimum structure has been determined, the microcavity OLED devices can be fabricated and characterized, and comparisons between experiments and theory can be made. © 2006 IEEE.