High-efficiency electron injection cathode of Au for polymer light-emitting devices

Polymer light-emitting diodes (PLEDs) have attracted great interests recent years due to their potential application in next generation large-area flat-panel displays. For these devices, however, achieving efficient electron injection from air- and chemicals-stable cathode remains a great challenge. Here we demonstrate for first time that by incorporation of a thin layer of amino-alkyl-substituted polyfluorene copolymer spin-coated from alcohol or water solution, Au, a most noble metal with high work-function, can be a good electron injection cathode. This new type of bilayer cathode can significantly enhance electron injection to red, green and blue electroluminescent (EL) polymers, thereby resulting in high efficiency polymer LEDs, which are comparable to that of using low work-function metals, such as Ca and Ba as cathode. The use of most stable metals such as Au as cathode will open a door for fabrication and patterning of air-stable flat panel displays.