Electroluminescence of LEDs consisting two layers of Alq3 and high Tg, blue-light emitting branched compounds

Two high glass transition (T-g) (>250degreesC) organic Compounds, Cz3d and tris-[4-(2-{4-[3,6-bis(4-t-butylphenyl)cabazole-9-yl]phenyl vinyl)phenyl]amine (TPA-Cz3d), containing three carbazole moieties were utilized in the construction of bilayer devices consisting of the compounds and tris(8-hydroquinolino)aluminum (Alq(3)) layers. TAP-Cz3d has the triphenyl amine moiety as a core. They themselves performed poorly as blue-light emitters in single layer LEDs. The bilayer devices revealed much improved electroluminescence (EL) properties emitting light of maximum brightness of 7400-13,000 Cd/m(2) with an external quantum efficiency approaching 0.6%. But emitted light of the bilayer devices was not from the organic layer but was front Alq3 layer indicating that the two compounds was efficient hole transporters. In all the devices, indium tin oxide (ITO)-coated glass and a Li/Al alloy were utilized as anode and cathode, respectively. (C) 2003 Elsevier B.V. All rights reserved.