Highly Efficient Green Phosphorescent Organic Light Emitting Diodes with Improved Efficiency Roll-Off

A 10-nm thick 4,4',4 ''-tris(carbazole-9-yl)tri-phenylamine (TcTa) interlayer effectively confines triplet excitons within the emissive layer (EML) of phosphorescent organic light emitting diodes (PHOLEDs) based on green-emitting Ir(ppy)(3) dopant and improves the charge balance in the EML of the device, resulting the higher device efficiencies of 61.7 cd/A, 19.7 %, and 43.2 lm/W with the maximum luminance of 75,310 cd/m(2) and highly improved efficiency roll-off (22.2% at 20 mA/cm(2)) when compared to those (61.1 cd/A, 19.6 %, and 47.2 lm/W with a maximum luminance of 38,350 cd/m(2)) of the standard device with efficiency roll-off of 62.3 % at 20 mA/cm(2).