Highly efficient phosphorescence from organic light-emitting devices with an exciton-block layer

One of the keys to highly efficient phosphorescent emission in organic light-emitting devices is to confine triplet excitons generated within the emitting layer. We employ starburst perfluorinated phenylenes (C60F42) as a both hole- and exciton-block layer, and a hole-transport material 4,4',4'-tri(N-carbazolyl) triphenylamine as a host for the phosphorescent dopant dye in the emitting layer. A maximum external quantum efficiency reaches to 19.2%, and keeps over 15% even at high current densities of 10-20 mA/cm(2), providing several times the brightness of fluorescent tubes for lighting. The onset voltage of the electroluminescence is as low as 2.4 V and the peak power efficiency is 70-72 lm/W, promising for low-power display devices. (C) 2001 American Institute of Physics.