Energy-level alignment at the tris-(8-hydroxyquinolate)-aluminum/Gd interface and Gd-electron-injection layer for organic electroluminescent device

The energy-level alignment for the tris-(8-hydroxyquinolate)-aluminum (Alq( 3))/Gd interface is determined by ultraviolet photoemission spectroscopy. T he energy difference between the Fermi level in Gd and the low-energy edge of the highest occupied molecular orbital in Alq(3) is 2.63 eV, and the vac uum level in the Alq(3) layer is moved upward to 0.35 eV with respect to it s intrinsic level. Gd/Al, Al:Li (0.1%), and Al were employed as a cathode f or the organic electroluminescent device. Among these devices, the device w ith the Gd-electron-injection layer has operated at the lowest voltage. (C) 2001 American Institute of Physics.