We report on the current-voltage (J-V) characteristics of single-layer devices employing pure and heavily TTN-doped Alq(3) films as active layers. In the undoped device, the current is limited by the carrier injection at the Mg/Alq(3) interface with a small injection barrier. In the uniformly-doped device, the current flow is much larger and behaves as space-charge-limited current (SCLC). This means a conversion from injection-limited to bulk-limited current. As the interface- and uniformly-doped devices show similar magnitude of current, the improvement of the current is ascribed to the large enhancement of electron injection due to the doping-induced modification of the interfacial electronic structure. (c) 2006 Elsevier B.V. All rights reserved.