A thermally stable hole injection material for use in organic light-emitting diodes

A thermally stable hole injection material, 4,4'-bis-(3,5-bis-(diphenylamino)-phenyl)-1,1'-binaphthyl(PPBN), was synthesized and the device performances of the organic light-emitting diodes(OLEDs) with PPBN as a hole injection layer were investigated. Glass transition temperature of PPBN could be enhanced to 148 degrees C by the introduction of a rigid diphenylbinaphthyl core in the molecular structure. The use of PPBN as a hole injection layer for OLEDs lowered the driving voltage and enhanced the light-emitting efficiency. The power efficiency of PPBN based devices with tris(8-hydroxyquinoline)aluminium as an emitting material could be improved by 80% compared with that of 4,4',4 ''-tris(2-naphthylphenylamino)triphenylamine based devices. (C) 2007 Elsevier B.V. All rights reserved.