Sputter deposition of cathodes in organic light emitting diodes

Sputter deposition was employed for cathode preparation in organic light em itting diodes (OLEDs). A thin film of copper phthalocyanine (CuPc) was foun d to be an effective buffer layer in preventing sputter damage to the OLED layer structure. However, the CuPc layer forms an electron-injection barrie r with the underlying Alq layer, resulting in increased electron-hole recom bination in the nonemissive CuPc layer, and thus a substantial reduction in electroluminescence efficiency. Incorporation of Li at the CuPc/Alq interf ace from a sputter-deposited Al (Li) cathode was found to reduce the inject ion barrier at the interface and make the overall device efficiency compara ble to a device having an evaporated MgAg cathode. The devices exhibited go od operational stability with a half lifetime greater than 3800 h at 20 mA/ cm(2). (C) 1999 American Institute of Physics. [S0021-8979(99)08520-5].