Highly efficient blue electrophosphorescent devices with a novel host material

Highly efficient blue electrophosphorscent light emitting diodes with a new host material N,N'-dicarbazolyl-1,4-dimethene-benzene (DCB) were demonstrated. The energy transfer mechanism of the host-guest material system consisting of DCB and bis[(4,6-difluorophenyl)-pyridinato-N,C-2'] (picolinato) Ir(III) (FIrpic) is an exothermic process. The device with a configuration of indium tin oxide/ N,N'-diphenyl-N,N'-bis(1,1'-biphenyl)-4,4'-diamine (NPB)/DCB:FIrpic/4,7-diphenyl-1,10-phenanthroline(BPhen)/Mg:Ag was optimized by adjusting the thickness of emitting layer and the dopant concentration. The device with the 8% (weight ratio) FIrpic and 30 nm emitting layer exhibits the maximum external quantum efficiency and current efficiency of 5.8% and 9.8 cd/A, respectively, at the luminance of 22 cd/m(2) driven at the voltage of 6.0 V. (C) 2004 Elsevier B.V. All rights reserved.