Electronic structures of the 8-hydroxyquinoline aluminum(Alq3)/LiF/AlandAlq3/Alinterfaces were measured by ultraviolet photoelectron spectroscopy. Shifts of the highest occupied molecular orbital level and the vacuum level of theAlq3layer due to insertion of a thin LiF layer were observed. This result indicates that the thin LiF layer at theAlq3/Alinterface reduces barrier height for electron injection from the Al toAlq3.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. ©1998 American Institute of Physics.