Multilayer organic electrophosphorescent white light-emitting diodes without exciton-blocking layer

We demonstrate high-efficiency white organic light-emitting diodes with two emissive layers, in which different hosts are employed. With the energy gap of the two hosts, there was no exciton-blocking layer between the emissive layers to confine the diffusion of excitons. The phosphorescent dye, bis[(4,6-difluorophenyl)-pyridinato-N, C-2'] (picolinato) Ir(III) and bis (1-phenyl-isoquinoline) (acetylacetonate) iridium (III) [Ir(pic)(2)acac] were employed as guests, while N,N-'-dicarbazolyl-1, 4-dimethene-benzene and 4, 4(')-N, N-'-dicarbazole-biphenyl were employed as hosts, respectively. The device exhibited white emission by controlling the thickness of the emissive layers and the maximum current efficiency and luminance were 10.5 cd/A and 22 000 cd/m(2), respectively. (c) 2006 American Institute of Physics.