ELECTRON-SPECTROSCOPY STUDIES OF INTERFACE FORMATION BETWEEN METAL-ELECTRODES AND LUMINESCENT ORGANIC MATERIALS

Using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), pie have studied the formation of metal/organic interfaces in organic electroluminescent devices. Oligo (p-phenylenevinylenes) (OPV) and tri s-(8-hydroxyquinoline)aluminum (Alq(3)) were used as the organic mater ials and Ca was used as the metallic layer. Interfaces are formed diff erently by depositing organic layer on Ca and Ca on organic substrate. For Ca/OPV, UPS revealed a clear evidence for interface state formati on upon Ca deposition. The evolution of XPS core level peak as a funct ion of Ca layer thickness was consistent with the energy level bending picture, The XPS and UPS spectra for OPV/Ca as a function of organic layer thickness also confirmed the energy level bending. The data obta ined allowed us to deduce the energy level diagram near the interface. Similar data for Alq(3)/Ca indicated that no electron injection barri er exists at this interface if the Alq(3) optical band gap in the lite rature was used for estimating the energy position of the lowest unocc upied state. (C) 1997 American Vacuum Society.