UV PHOTOEMISSION-STUDY OF 8-HYDROXYQUINOLINE ALUMINUM (ALQ(3)) METAL INTERFACES/

Electronic structure of tris(8-hydroxyquinolino) aluminum (Alq(3)) / m etal interface was directly investigated as a model interface of elect roluminescent (EL) devices by UV photoemission spectroscopy (UPS). Sim ulated spectrum of Alq(3) calculated by a MNDO / PM3 molecular orbital calculation showed a good correspondence with the observed UPS spectr um. Highest occupied molecular orbitals (HOMOs) of Alq(3) was assigned to HOMO of the ligands. At Alq(3) / metal interfaces, shift of the va cuum level was observed, in contrast to the traditional assumption wit h common vacuum level at the interface. Interfacial energy diagrams de termined by the results of UPS corresponds well to actual carrier-inje cting character at the interface.