Efficient electrophosphorescence using a doped ambipolar conductive molecular organic thin film

We demonstrate a high efficiency organic electrophosphorescent device comprised of a 4,4',4 ''-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA) hole transport layer and a 4,4'-N,N'-dicarbazole-biphenyl (CBP) host doped with the metallorganic phosphor, fac-tris(2-phenylpyridine)iridium (Ir(ppy)(3)) as the green light-emitting layer. The device exhibits peak external quantum and power efficiencies of (12.0 +/- 0.6)% and (45 +/- 2) lm/W, respectively, corresponding to similar to 60% internal quantum efficiency. A luminance of 1850 cd/m(2) is observed at a current density of 10 mA/cm(2). The device operating properties are controlled by electron injection into, and transport by the CBP layer along with hole injection from m-MTDATA directly into the Ir(ppy)(3) highest occupied molecular level, leading to direct carrier recombination and exciton formation on the phosphor dopant. Ambipolar conduction properties of the Ir(ppy)(3):CBP layer are established by analysis of triplet-triplet annihilation, exciton formation and the luminance current voltage characteristics. (C) 2001 Published by Elsevier Science B.V.