Organic light emitting diode (OLED) devices were developed using a CuPc/metal/Al multilayer structure as cathode, and Li, Ca, and Mg were employed as metals. The typical device structure is composed of a glass substrate/indium tin oxide (ITO)/N, N'-diphenyl-N, N'-(3-methyl phenyl)-1, 1'-biphenyl-4, 4'-diamine (TPD)/tris (8-quinolinolato) Al (Alq(3))/copper phthalocyanine (CuPc)/metal/Al. The CuPc/metal/Al cathode can improve the performance of OLEDs by decreasing the turn-on voltage and increasing the efficiency of the device. A comparable luminous efficiency can be reached in the device structure ITO/TPD/Alq(3)/CuPc/Li/Al as compared with the LiF/Al bilayer cathode one. The mechanism of CuPc/metal/Al cathode in OLED devices is discussed in this paper. (c) 2008 The Electrochemical Society.