We report highly efficient green phosphorescent devices comprising a triplet exciton confinement configuration, using 4,4'-N,N'-dicarbazoleterpheyl(CTP) as a narrow band-gap host and high triplet energy charge transporting layers. Maximum current and power efficiencies of 56.89 cd/A, and 48.22 lm/W (external quantum efficiency of 18.0%) are demonstrated by optimizing the doping concentration. Such high efficiency is attributed to good confinement effect of triplet excitons by narrow band-gap CTP host with reasonable doping concentration and introduction of good exciton blocking layers at the emitting layer interfaces. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.