Emission process in bilayer organic light emitting diodes

Efficient organic light emitting devices (OLEDs) using methyl substituted ladder-type poly (paraphenylene) (m-LPPP) and tris(8-hydroxy) quinoline aluminum (Alq(3)) as active materials are presented. For bilayer OLEDs the emissive region is found to be in both layers adjacent to the m-LPPP/Alq(3) interface. The performance of these hybrid devices with constant m-LPPP thickness and varying Alq(3) thickness is compared to that of a single layer m-LPPP device by investigating the relative spatial distribution of the light emission. The relation between the intensity of the light emitted from each layer and the distance to the cathode metal is discussed. Furthermore, the m-LPPP emission is also affected by the internal electric field at the interface. (C) 1998 American Institute of Physics. [S0003-6951(98)04042-X].