Development of fullerene-containing composites for organic light-emitting devices

In order to widen the practical applications of Organic Light Emitting Devices (OLEDs), the device efficiency and device stability must be improved. The anode structure of an OLED device, including the anode and the adjacent contacting organic layer, plays important roles in both device efficiency and stability issues. In this study, C60 is used to engineer the anode structure by incorporating C60 into common hole transport materials, forming organic-C60 composites.;Copper phthalocyanine (CuPc):C60 composites have been studied for use with Au anodes. When the Au/CuPc:C60 composite anode structure at an optimum C60 composition of 30 wt.% is used to replace the conventional ITO/CuPc anode structure, a significant increase in current efficiency (∼2 times) is achieved. This result suggests a new possibility to replace the problematic ITO anode with an Au anode. Moreover, the CuPc:C60 composites also form efficient hole injection structures with other metals, namely, Ag, Mg, and Al. The versatility of the composite anode structure is attributed to the complementary role of the two constituents: C60 facilitates hole injection from the metals to the composite; CuPc plays the primary role of transferring holes from the composite to the hole transport NPB layer.;The composites enable more thermally stable anode structures as concluded by annealing experiments. It is found that the main reason for the improved thermal stability of the composite anode structure is not interface modification, but the higher thermal stability of the composite materials. No chemical interaction between the components of the composites is detected.;N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB):C 60 composites have been studied for use with indium tin oxide (ITO) anodes. Compared with a conventional device without C60, the composite device at a C60 composition of 10 wt.% has improved efficiency by 25% due to more balanced electron-hole currents.