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

Exciplex emission has been suppressed by doping an emitter in an electron-transporting host in blue organic light-emitting diodes. The dopant, 5,5′-bis(dimesitylboryl)-2,2′-bithiophene (BMB-2T), was a thermally stable electron-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′-diphenyl-[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/m2 at a current density of 240 mA/cm2 and with a pure blue emission peaking at 446 nm (chromaticity coordinates: x=0.15, y=0.12) at 3 wt.% dopant concentration.