Efficient electrofluorescent organic light-emitting diodes by sequential doping

The authors reported a highly efficient electrofluorescent organic light-emitting diode fabricated by sequential doping. An archetypal device utilizing 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran as dopant in a matrix of tris-(8-hydroxyquinoline) aluminum was investigated. The emission layer consists of a few repeating cells, similar to a multiple quantum well structure, which are made of sequentially evaporated host and dopant. An external quantum efficiency as high as 3.38% photons/electron was obtained. By avoiding coevaporation, sequential doping should render better control on device performance and day-to-day repeatability. (C) 2007 American Institute of Physics.