Electronic structure of 8-hydroxyquinoline aluminum/LiF/Al interface for organic electroluminescent device studied by ultraviolet photoelectron spectroscopy

Electronic structures of the 8-hydroxyquinoline aluminum (Alq(3))LiF/Al and Alq(3)/Al interfaces were measured by ultraviolet photoelectron spectroscopy. Shifts of the highest occupied molecular orbital level and the vacuum level of the Alq(3) layer due to insertion of a thin LiF layer were observed. This result indicates that the thin LiF layer at the Alq(3)/Al interface reduces barrier height for electron injection from the Al to Alq(3). We, therefore, conclude that lowering of the driving voltage in an organic electroluminescent device with a thin LiF layer is attributable to the reduction of the barrier height. (C) 1998 American Institute of Physics. [S0003-6951(98)00345-3].