STUDY OF INTERFACIAL DEGRADATION OF THE VAPOR-DEPOSITED BILAYER OF ALQ3/TPD FOR ORGANIC ELECTROLUMINESCENT (EL) DEVICES BY PHOTOLUMINESCENCE

The interfacial change of a vapor-deposited TPD (N, N'-diphenyl-N, N'-bis-(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine) and Alq(3) (Tris-(8-hydroxyquinoline) aluminum) bilayer film was characterized by photoluminescence (PL) in the temperature range from room temperature to 80 degrees C under an ambient atmosphere. The TPD and the Alq(3) film are widely used as a hole transport and an emitter layer, respectively, in organic electroluminescent (EL) devices (ITO/TPD/Alq(3)/metal). As the substrate plate, a slide glass was used in this work. In an Alq(3)/TPD bilayered structure, two PL bands from Alq(3) and TPD were observed and the relative PL intensity of Alq(3) to that of TPD was increased with time. The change was accelerated with increasing temperature. In case of a co-deposited single layer of TPD and Alq(3), an Alq(3) PL band predominated and, in addition, the PL intensity was not changed remarkably with increasing temperature. These results support that the PL change observed for the Alq(3)/TPD bilayered structure is ascribed to quenching of photo-excited TPD by Alq(3) as a result of diffusion of the components into each other layer.