Electronic structure and energy level alignment of Alq3/Al2O3/Al and Alq3/Al interfaces studied by ultraviolet photoemission spectroscopy

The electronic structures at the interface of aluminum tris(8-hydroxyquinoline) (Alq3)/Al2O3/Al have been determined by ultraviolet photoemission spectroscopy measurements and compared to similar measurements of the Alq3/Al interface. In the Alq3/Al2O3/Al study, shift of the highest occupied molecular orbital level of the Alq3 layer was observed when compared to that of Alq3/Al. An energy level alignment diagram was proposed, showing that the lowering of the driving voltage achieved in organic electro-luminescent devices with a thin Al2O3 layer between the aluminum cathode and the Alq3 ®lm can be attributed to the reduction of the barrier height for electron injection. Th