Efficient red organic light-emitting diode sensitized by a phosphorescent Ir compound

The efficiencies of red organic light-emitting diode (OLED) using tris-(8-hydroxy-quinoline)aluminum (Alq(3)) as host and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as dopant were greatly increased by adding a small amount (0.3 wt%) of Ir compound, iridium(III) bis(3-(2-benzothiazolyl)-7-(diethylamino)-2H-1-benzopyran-2-onato-N-',C-4) (acetyl acetonate) (Ir(C6)(2)(acac)), as a sensitizer. The device has a sandwiched structure of indium tin oxide (ITO)/4,4('),4('')-tris (N-(2-naphthyl)-N-phenyl-amino)triphenylamine (T-NATA) (40 nm)/N,N-'-bis(1-naphthyl)-N,N-'-diphenyl-1,1(')-biphenyl-4,4(') diamine (NPB) (40 nm)/Alq(3):DCJTB (0.7 wt%):Ir(C6)(2)(acac) (0.3 wt%) (40 nm)/Alq(3) (40 nm)/LiF (1 nm)/Al (120 nm). It can be seen that the current efficiencies of this device remained almost (13.8 +/- 1) cd/A from 0.1 to 20,000 cd/m(2) and the Commission International d'Eclairage (CIE) coordinates at (0.60, 0.37) in the range of wide brightness. The significant improvement was attributed to the sensitization effect of the doped Ir(C6)(2)(acac), thus the energy of singlet and triplet excitons is simultaneously transferred to the DCJTB. (C) 2007 Elsevier B.V. All rights reserved.