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) (Ir(piq)(3)) 15wt% doped into two different host molecules, 4,4'-bis[N-(1-napthyl)-N-phenyl-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 cd/m(2) have been measured.