A diamond-like carbon （DLC） film is deposited as an electron injection layer between the polymer light-emitting layer（MEH-PPV） and aluminum （Al） cathode electrode in polymer electroluminescence devices （PLEDs） using a radio frequency plasma deposition system. The source material of the DLC is n-butylamine. The devices consist of indium tin oxide （ITO）/MEH-PPV/DLC/Al. Electron injection properties are investigated through I-V characteristics,and the mechanism of electron injection enhancement due to a thin DLC layer has been studied. It is found that： （1） a DLC layer thinner than 1.0nm leads to a higher turn-on voltage and decreased electroluminescent （EL） efficiency; （2） a 5.0nm DLC layer significantly enhances the electron injection and results in the lowest turn-on voltage and the highest EL efficiency; （3） DLC layer that exceeds 5.0nm results in poor device performance;and（4） EL emission can hardly be detected when the layer exceeds 10.0nm. The properties of ITO/MEH-PPV/DLC/Al and ITO/MEH-PPV/LiF/Al are investigated comparatively.
