Photoemission spectroscopy study of Alq3 and metal mixed interfaces

The electronic structures of mixed layers of tris (8-hydroxy-quinoline) aluminum (Alq3) and metal (Au and Al) were studied by ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The devices with a mixed layer between Alq3 and the cathode were fabricated. The barrier height for electron injection was reduced by doping metals (Au or Al) into Alq3. The doping enhanced the performance of the device. From the XPS study, the doped Au metal did not react with Alq3 and in addition, the doped Al metal reacted slightly with Alq3. From the UPS study, the highest occupied molecular orbit shifted to a higher binding energy for both metal mixed layers. From these studies, it is concluded that the enhanced device characteristics come from the barrier height reduction by the metal doped in Alq3 rather than from the charge transfer complex induced by the reaction of Alq3 and metal. (C) 2001 American Institute of Physics.