A theoretical and experimental investigation of light extraction from polymer light-emitting diodes

Using numerical modeling techniques we predict the emission into air, substrate, polymer/indium tin oxide (ITO), and surface-plasmon modes of a polymer light-emitting diode. The results give good insight into the possible efficiency increases that can be expected for various light extraction techniques. In addition, the effects of various optical properties and layer thicknesses on the optical performance of the device are reported. We show how modification of the substrate can be used to concentrate light into mode types from which light can be easily extracted. We then report experimental results for two very different light extraction techniques. First, we demonstrate how Bragg gratings can be used to extract light from waveguide modes in the polymer/ITO layers. With an optimized Bragg grating, we have increased the external power efficiency by 25% at high brightness levels. In addition, we have used substrate-shaping techniques to extract light from waveguide modes in the glass substrate. In this case, we were able to increase the efficiency by over 60%. Finally, we compare our numerical and experimental results to summarize the possible benefits of various light extraction strategies. (C) 2005 American Institute of Physics.