Study of interfacial degradation and morphological change of the vapor-deposited bilayer of Alq3/TPD for organic electroluminescent devices by AFM and PL technique

The morphological change of vapor-deposited films of TPD (N, N'-diphenyl-N, N'-bis-(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine) and Alq3 (Tris-(8-hydroxyquinoline) aluminum) and the interfacial degradation of Alq3/TPD bilayer were characterized by atomic force microscopy (AFM) and fluorescence spectroscopy, respectively, in the temperature range from room temperature to 80 degrees C under an ambient atmosphere. The TPD and the Alq3 film are widely used as a hole transport and an emitter layer, respectively, in an organic electroluminescent device (an indium tin oxide (ITO) coated glass/TPD/Alq3/metal). As the substrate plate, an ITO coated glass or a slide glass was used in this work. The relative photoluminescence (PL) intensities of Alq3 to that of TPD in an Alq3/TPD and a TPD/Alq3 bilayer were increased with time. The changes were accelerated with increasing temperature and ascribed to quenching of photo-excited TPD by Alq3 diffusing into the TPD layer.