Very Long Operational Lifetime at High Initial Luminance of Deep Red Phosphorescent Organic Light-Emitting Diodes With Double Emission Layers

We report a double emission layer structure, incorporating a double phosphorescent “guest/host system” of tris (1-Phenylisoquinoline) iridium (III) $({\hbox{Ir}}({\hbox{piq}})_{3})$ 15wt% doped into two different host molecules, ${\hbox{4,4}}^{\prime}-{\hbox{bis}}[{\hbox{N}}-(1-{\hbox{napthyl}})-{\hbox{N}}-{\hbox{phenyl}}-{\hbox{amino}}]$ biphenyl (NPB) and bis-(2-methyl-8-quinolinolato)-4-(phenyl-phenolato) aluminum-(III) (BAlq). The proposed configuration reduces the efficiency rolloff, providing high stability at high operating luminance. A maximum current efficiency of 9.5 cd/A, at a driving voltage of 3 V, and a remarkably long device lifetime of more than 2500 h at a starting luminance of 6000 ${\hbox{cd/m}}^{2}$ have been measured.