AbstractWe 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-dimethyl-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/m2 at V=12 V, J=490 mA/cm2. Maximum efficiency was 20 lm/W at 3.1 mA/cm2.
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