Highly efficient organic light-emitting diodes with metal/fullerene anode

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 $(∼10V)$ 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.