Phosphorescent Organic Light-Emitting Diodes with Simplified Device Architecture

We demonstrated that single-layered red phosphorescent organic light-emitting diodes (OLEDs) can have high a efficiency without carrier transport and injection layers This high efficiency is caused by the direct injection of carriers from electrodes into a dopant, bis(2-phenylquinoline) indium(III) (acetylacetonate) [Ir(ppy)(2)(acac)] This mechanism is proved by analyzing the single-layered devices with various hosts, 4,4'-N,N'dicarbazole-biphenyl (CBP), 9-phenyl-3[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-9H-carbazole (LPGH 114), 9-(naphthalen-2-y1)-344-(1-phenyl-1/-1-benzoldjimidazol-2-yl)phenyl]-9H-carbazole (LPGH 124), and 9-pheny1-3,6-bis[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-9H-carbazole (LPGH 153) Among the devices, the single-layered device with LPGH 153 shows a luminous efficiency, a power efficiency, and a quantum efficiency of 9 3 cd/A, 5 2 lm/W, and 6 2%, respectively The single-layered device with CBP was compared with a multilayered device with CBP As a result, the single-layered device shows a reduced operating voltage, an enhanced roll-off efficiency. and a pure emitting color in comparison with the multilayered device owing to the direct injection of carriers into a dopant and the suppression of exciplex formation (C) 2010 The Japan Society of Applied Physics