We report on the reduction of driving voltage in organic electrophosphorescent devices with mixed hole transport material as emission layer. The emission layer was mixed with N,N'-diphenyl-N,N'-(3-methylphenyl) -[1,1'-biphenyl]-4,4'-diamine (TPD) as a hole-transport material.. 4,4'-bis(9-carbazolyl)-biphenyl (CBP) as a host material for a phosphorescent material, tris(2-phenylpyridine) iridium (Ir(ppy)(3)) as a phosphorescent material and 2,9-dimetliyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine: BCP) as an electron-transport material. The emission occurred from Ir(ppy)(3) and was independent on the ratio of TPD and CBP. For triple-layered device with the TPD:CBP mixing ratio of 10:90, maximum luminance obtained was 104,000 cd/m(2) at V = 12 V, J = 490 mA/cm(2). Maximum efficiency was 20 lm/W at 3.1 mA/cm(2). (c) 2004 Elsevier B.V. All rights reserved.