Highly efficient organic light-emitting diodes using novel hole-transporting materials

A new class of tetraminobiphenyl derivatives, which contains a 3,3′,5,5′-tetraminobiphenyl core, has been synthesized and examined as a hole-transporting material for organic light-emitting diodes. We fabricated the organic light-emitting diode (OLED) cells with tetraminobiphenyl derivatives as hole-injecting layer, hole-transporting layer and hole-injecting and transporting layer for green device with tris(8-quinolinolato)aluminum (Alq3) doped with 1% of Coumarin 545T (C545T) as green emitting layer. Tetraminobiphenyls were found to be useful as a novel hole-transporting material. The electroluminescent device with the 3,3′,5,5′-tetrakis(p-tolyldiamino)biphenyl (TTAB) as a hole-transporting layer was more efficient than that with the analogous triarylamine, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl benzidine (NPB). The external luminous efficiency of the device IV having TTAB as one hole-injecting and transporting layer can reach 14.55 cd/A, which is higher than the standard device I (11.66 cd/A) using two layers, a hole-injecting layer and a hole-transporting layer.