Polybenzobisazoles Are Efficient Electron Transport Materials for Improving the Performance and Stability of Polymer Light-Emitting Diodes

A series of seven polybenzobisazoles were investigated as electron transport materials in arylene vinylene polymer-based electroluminescent devices. A large enhancement in performance and stability was observed in poly( p -phenylene vinylene) and poly(2-methoxy-5(2‘-ethyl-hexyloxy)-1,4-phenylene vinylene) light-emitting diodes by using polybenzobisthiazoles and poly( p -phenylene benzobisoxazole) as electron-transport materials. Devices using polybenzobisazole electron transport layers and aluminum cathodes had a turn-on voltage as low as 2.8 V, a luminance of up to 1400 cd/m 2, and an external quantum efficiency of up to 2.5%. These polymer devices and their performances were stable under repeated testing over a period of 9−10 months storage in air. The superior performance of the polybenzobisazole thin films as electron-transport and hole-blocking materials in polymer light-emitting diodes is due to their high glass-transition temperature, environmental resistance, and photochemical/electrochemical stability. These results demonstrate that robust high-temperature polybenzobisazoles can be used as efficient electron-transport and hole-blocking materials for improving the performance and stability of polymer light-emitting devices.