Improved color purity and efficiency of blue organic light-emitting diodesvia suppression of exciplex formation

Exciplex emission has been suppressed by doping an emitter in an electron-t ransporting host in blue organic light-emitting diodes. The dopant, 5,5'-bi s(dimesitylboryl)-2,2'-bithiophene (BMB-2T), was a thermally stable electro n-transporting material with a high fluorescence quantum efficiency. BMB-2T was doped into a trimer of N-arylbenzimidazoles (TPBI) which functioned as the host and electron-transporting layer. N,N'-bis(3-methylphenyl)-N,N'-di phenyl-{1,1'-biphenyl]-4,4'-diamine (TPD) was used as the hole-transporting layer. The device, with a structure of indium tin oxide (ITO)/TPD/TPBI:BMB -2T/TPBI/Mg:Ag, showed a bright emission of 2200 cd/m(2) at a current densi ty of 240 mA/cm(2) and with a pure blue emission peaking at 446 nm (chromat icity coordinates: x=0.15, y=0.12) at 3 wt.% dopant concentration. (C) 2001 Elsevier Science B.V. All rights reserved.