Efficient and stable organic light-emitting diodes with a sputter-deposited cathode

Sputter deposition was employed for cathode preparation in organic light-emitting diodes (OLEDs). Although a thin film of copper phthalocyanine (CuPc) can act as an effective buffer layer in preventing sputter damage to the OLED layer structure, it forms an electron-injection barrier with the underlying Alq layer. Incorporation of Li at the CuPc/Alq interface by sputter deposition of Li-doped Al on CuPc can lower the injection barrier and drastically increase the overall device efficiency. The resulting devices shows both optical and electrical characteristics comparable to a device with a thermally evaporated MgAg cathode and exhibits superior operational stability with a half-life time of about 4000 h at 20 mA/cm(2). The potential application of using this structure is further demonstrated in replacing Alq with CuPc for electron transport. (C) 2000 Elsevier Science S.A. All rights reserved.