Conditions of recombination zone splitting in organic light-emitting diodes

We present a theoretical and experimental study of a multilayer organic light emitting device (OLED) with a partially doped emission layer. An extended version of our established "MOLED" device model is used to understand the effects of the partially doped layer on the transport behavior and on the radiative charge recombination distribution as a function of applied bias. A step by step discussion of the possible mechanisms that can be introduced by doping and the resulting changes on the device properties is presented. We have found that under certain conditions the recombination zone is split into two zones leading to an emission color change with increasing voltage. By using the yellow emitting laser dye derivative 4-(dicyanomethylene)-2-methyl-6-{2-[(4diphenylaminophenyl]ethyl}-4H-pyran (DCM-TPA) with electron trapping capabilities as a dopant in a standard organic light emitting device, we have achieved high quantum efficiency with excellent color saturation. Furthermore, for this special case a blue-shift of the emission color is observed for increasing bias due to the appearance of a double peak structure of the recombination zone.