In organic light emitting diodes (OLEDs) with transparent electrodes, the luminance usually becomes inhomogeneous if the size of the pixel increases above 10mm. A theoretical model for inhomogeneous voltage and luminance in OLEDs is provided together with an approximate analytical solution for the problem in case of cylindrical symmetry. Experimental observations of inhomogeneous luminance are compared with numerical simulations based on the theoretical model, proving the applicability of the approximations made in the theoretical model.

The outcoupling of light in organic light-emitting devices is one of the limiting parameters for obtaining a high external efficiency. A simple geometrical model is presented that allows one to estimate the importance of optical parameters such as mirror reflectivity, scattering probability, and device structure. The model allows the derivation of analytical expressions for the outcoupling efficiency in some simplified cases.

We present simulation and experimental results to achieve increased light extraction of a substrate emitting OLED. We present a comparison between a grating surface on the OLED and an array of microlenses at the interface between substrate and air. This experimentally gives -in both cases-a relative improvement of approx. 30 %. We also demonstrate the concept of a RC 2 LED, applied to an OLED. The RC 2 LED is composed by adding a high, low and high index layers between ITO and glass, i.e. the interface between organic layers and glass. These extra layers create a cavity which numerically gives a relative improvement of over 60% at the resonance wavelength of the cavity over a wavelength range of 50-100 nm. The influence of an array of micro lenses in addition to the RC 2 layers is also investigated in this paper.

We present simulation and experimental results to achieve increased light extraction of a substrate emitting OLED. A 2D grating located at the glass-air interface experimentally gives a relative improvement of approx. 30 %.