Highly efficient blue-light-emitting diodes from polyfluorene containing bipolar pendant groups

Abstract

A highly efficient blue-light-emitting copolymer with bulky hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) pendant groups at the C-9 position of fluorene was synthesized. The results from photoluminescence and electrochemical measurements reveal that both the side chains and the polyfluorene main chain retain their own electronic characteristics in the copolymer. It shows a pure blue emission with no aggregates or excimers formed even after being annealed at 150 degreesC under nitrogen for 20 h. In addition, it also demonstrates improved charge injection and balanced charge transport in electroluminescence. The maximum external quantum efficiency of a single-layer device using this copolymer as the emitting layer is 1.21% (at a brightness of 354 cd/m(2) with driving voltage of 7.6 V). The maximum luminance of the device reaches 4080 cd/m(2) at a bias of 12.0 V and a current density of 640 mA/cm(2).