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Metal/fullerene bilayers have been studied as hole injection electrodes for use in organic light-emitting diodes (OLEDs). In the case of a simple emission zone structure, it is found that OLEDs with the Au/C60 anodes have much lower (∼10 V) driving voltages and much higher current efficiencies (five times higher) than OLEDs with a simple Au anode. This anode structure was found to be applicable for all types of light-emitting structures including fluorescent and phosphorescent dye-doped systems. The formation of a primary bond at the Au/C60 interface is explained as the major cause for efficient hole injection from Au to C60. The hole transfer barrier between C60 and the adjacent hole transport layer is also found critical in selecting suitable matching materials to achieve highly efficient OLEDs. [ABSTRACT FROM AUTHOR]