Electron Injection Enhancement by Diamond-Like Carbon Film in Polymer Electroluminescence Devices

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.