Electronic structure and energy level alignment of Alq(3)/Al2O3/Al and Alq(3)/Al interfaces studied by ultraviolet photoemission spectroscopy

The electronic structures at the interface of aluminum tris(8-hydroxyquinol ine) (Alq(3))/Al2O3/Al have been determined by ultraviolet photoemission sp ectroscopy measurements and compared to similar measurements of the Alq(3)/ Al interface. In the Alq(3)/Al2O3/Al study, shift of the highest occupied m olecular orbital level of the Alq(3) layer was observed when compared to th at of Alq(3)/Al. An energy level alignment diagram was proposed, showing th at the lowering of the driving voltage achieved in organic electro-luminesc ent devices with a thin Al2O3 layer between the aluminum cathode and the Al q(3) him can be attributed to the reduction of the barrier height for elect ron injection. The electronic structures of Alq(3) grown on Ga and its oxid e have also been studied. (C) 2000 Elsevier Science S.A. All rights reserve d.