Optical simulation of top-emission organic light-emitting devices with passivation layer

In this paper, we report simulation results of a top-emission organic light-emitting device (TOLED) with a passivation layer composed of silicon dioxide (SiO2) and silicon nitride (Si3N4) to protect organic layers from oxygen and moisture. Usually, the thickness of such a layer is about several micrometers. The electrode material of the device used for simulation is silver (Ag). The anode is thick and opaque while the cathode is thin and semi-transparent. The structure is capped with three pair of SiO2 and Si3N4 as the passivation layer. When SiO2 thickness is less than 2μm, the output intensity changes and the spectrum peak shifts. The peaks oscillate as a function of the SiO2 thickness and the period is about 170nm. When the SiO2 thickness is over 2μm, more than single peak are observed. With a simple model, we found that the frequency difference between two peaks corresponds to the free spectral range of the fabry-perot cavity formed by passivation layer. When a passivation layers is added on the TOLED, the microcavity effect results in the presence of multi-peaks. It limits the view angle and decreases the color purity.