Interface injection-limited carrier-transport properties of Alq₃

We have studied the carrier-transport properties of the amorphous organic material tris (8-hydroxyquinoline) aluminium (Alq₃) for Al and LiF/Al cathodes at room temperature. The investigation was made by the current-voltage characteristic measurements for different Alq₃ film thicknesses. It is found that the current-voltage characteristic has a linear dependence on the thickness of the Alq₃ film. The current density increases by several orders for a LiF/Al cathode over that of Al at a given bias voltage. The carrier-injection processes at the metal/organic contact dominate the current-voltage characteristics. The carrier injection seems to be limited by the charge hopping of interfacial molecular sites.