Angular dependence of the emission from low Q-factor organic microcavity light emitting diodes.

Microcavity light emitting diodes based on materials with broad emission spectrum, such as tris (8-hydroxyquinoline) aluminum (Alq3), typically exhibit a significant blue shift of the emission wavelength with increasing viewing angle. In this work, we investigate the influence of the organic layer thickness on the angular dependence of the emission spectrum in low Q-factor microcavity OLEDs. We demonstrate that for different organic layer thicknesses qualitatively different emission wavelength dependences on the viewing angle can be obtained in microcavity devices consisting of two organic layers, N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) as a hole transport layer and Alq3 as emitting layer. The devices with different organic layer thickness were characterized by electroluminescence, photoluminescence, reflectance, and transmission measurements and results compared with the model.