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. The 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 vacuum level in the Alq(3) layer is moved upward to 0.35 eV with respect to its intrinsic level. Gd/Al, Al:Li (0.1%), and Al were employed as a cathode for the organic electroluminescent device. Among these devices, the device with the Gd-electron-injection layer has operated at the lowest voltage. (C) 2001 American Institute of Physics.