We developed highly efficient yellowish-green emitting phosphorescent organic light emitting diodes based on tris[4-methyl-2-2(4'-trimethylsilylphenyl)pyridinel [Ir(msippy)(3)]. The device showed electroluminescence emission from the dopant emitter at 521 nm with CIE color coordinates of (0.32, 0.62). We investigated the roll of 4,4',4 ''-Tris(carbazol-9-yl)triphenylamine (TcTa) interlayer between hole transporting and emissive layers on the higher device performances using different hole transporting materials. TcTa interlayer in the device using Di(4-(N,N-ditolyl-amino)-phenyl]cyclohexane as hole transporting layer confines the excitons within the emissive layer and improves the charge balance, resulting in higher device external quantum efficiency of 25.6% and current efficiency of 84.4 cd/A with improved efficiency roll-off. (C) 2011 Elsevier B.V. All rights reserved.