Highly efficient and concentration-insensitive organic light-emitting devices based on self-quenching-resistant orange-red iridium complex

Orange-red phosphorescent organic light-emitting devices (PHOLEDs) with high efficiency and concentration insensitivity based on a novel iridium complex, bis[2-(biphenyl-4-yl)benzothiazole-N, C-2']iridium(III) (acetylacetonate) [(4Phbt)(2)Ir(acac)], were fabricated. With the heavily doped emissive layer (EML) of 4,4'-N,N'-dicarbazolyibiphenyl (CBP): (4Phbt)(2)Ir(acac) in a wide and easily controlled dopant concentration range from 12 wt% to 24 wt%, a maximum power efficiency of 29 lm/W and an external quantum efficiency of > 16% of the PHOLEDs were obtained, implying the insensitivity of electroluminescence (EL) properties to doping concentration. Meanwhile, a maximum power efficiency of 5.0 lm/W was achieved from a non-doped device with neat (4Phbt)(2)Ir(acac) as the EML, indicating a superior property of self-quenching resistance. The mechanism of direct exciton formation, in which exciton-formation regions are distributed throughout the EML, is responsible for the significant alleviation of triplet-triplet annihilation and superior EL performance. (C) 2014 Elsevier B.V. All rights reserved.