Determination of the emission zone in a single-layer polymer light-emitting diode through optical measurements

We study the emission zone in a single-layer polymer light-emitting diode. The emission zone is found by studying the angular distribution of the elec troluminescence. The emission is modeled by accounting for optical interfer ence. We account for birefringence of the anode layer in our model. The act ive polymer was, however, found to be isotropic. The anode consists of a si ngle-layer of the conducting polymer complex poly(3,4-ethylenedioxythiophen e) and poly(styrene sulfonate) (PEDOT-PSS), with enhanced conductivity. As a cathode we use plain aluminum. By using only PEDOT-PSS we avoid having a thin metal layer or indium-tin-oxide as the anode in the path of the escapi ng light. The active material is a substituted polythiophene with excellent film forming properties. A comparison between the experimental and calcula ted angular distribution of light emission from a single-layered polymer li ght-emitting diode was shown to be in good agreement for the spectral regio n studied. By assuming a distribution of the emission zone, we deduce the p osition as well as the width of the zone. (C) 2001 American Institute of Ph ysics.