Diamond-like carbon (DLC) is deposited as an electron injection layer between the organic layer and Al cathode electrode in organic electroluminescence devices (OLEDs) by the use of Cs+ ion gun sputter deposition system. The devices consist of; indium tin oxide/PEDOT:PSS/MEH-PPV/DLC/aluminum. Electron injection properties have been investigated by I-V characteristics at various deposition conditions and the mechanism of electron injection enhancement due to a thin DLC layer has been studied. The characteristics of DLC film deposited at various negative carbon ion energies are examined by Raman spectroscopy Optical microscope is also used to observe the Al surface after the light emission test. It is found that the sp(2)/sp(3) ratio and electron affinity of DLC film are varied as the carbon ion energy increases from 50 to 200 eV, which enhance the electron injection and improve the property of OLEDs. An order magnitude increase in current is obtained from DLC layer inserted devices and the device stability is also improved.