Device operation of polymer light-emitting diodes

Easy processing and mechanical flexibility make polymer light-emitting diodes (PLEDs) suitable candidates for large-area display applications. The understanding of the device properties of PLEDs is a key ingredient for further optimization. This article reviews a device model developed at Philips Research that describes the current and light generation of PLEDs as a function of applied voltage. The model is based on experiments carried out on poly(dialkoxy-p-phenylene vinylene) devices. The combination of the experimental results and model calculations have revealed that (1) the hole current is dominated by space-charge effects and a field-dependent mobility, (2) the electron current is strongly reduced by traps, and (3) the recombination process between the injected electrons and holes is of the Langevin-type. These results explain specific device properties of PLEDs such as a bias-dependent and temperature-independent electroluminescence efficiency (photon/carrier) and indicate directions for further improvement of the device performance.