Various thicknesses of magnesium fluoride (MgF2) ultrathin films were inserted between electroluminescence layer and cathode in poly(p-phenylene vinylene) (PPV)-based organic light-emitting devices. It is observed that device with 0.4 nm of MgF2 has the highest luminance and current efficiency. At 7 V operation, the current efficiency has improved by approximately 1.5 times as compared to the standard device. The increase in device current and the improvement in efficiency are due to increased electron injection, leading to more balanced hole and electron numbers. At the same time, device with a layer of MgF2 inserted between anode indium tin oxide and polyethylenedioxythiophene has also shown obvious improvement in performance. It is observed that the device with 0.4 nm of MgF2 in anode side has the highest luminance and current efficiency. The improvement of the device performance in anode side are due to smoothened interface which boosts hole injection and the fluoride ions doping the PPV materials resulting in an increase of its electron affinity which mitigates the electron and hole's number imparity. (c) 2006 Elsevier B.V. All rights reserved.