Top Emission Organic Light-Emitting Diodes with Double-Metal-Layer Anode

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In this study, we investigated the optimum thicknesses of organic light-emitting diode (OLED) layers using a high-reflectivity metal, Al, coupled with high-work-function alloys, e.g., AuSn, AuGe, and AuGeNi, as anodes, and LiF/Al/Ag multilayers as cathodes. The work function of a double-metal-layer, Al/AuGeNi (60/2 nm), was measured to be 4.7 eV, which is higher than that of a single Al layer of 4.2 eV. A high-work-function anode increased the number of holes injected from the anode into a hole transport layer and hence increased luminescence efficiency. After the optimization of each organic layer thickness, the device produced a maximum luminance of 2930 cd/m2 and a maximum luminance yield of 1.4 cd/A, which are the significant improvements of the performance characteristics of 537 cd/m2 and 0.28 cd/A obtained before the optimization of organic thickness, when the single Al layer was used as an anode, the device only exhibited a luminescence of 190 cd/m2 and a short lifetime.
2007-04-30