High efficiency polymer electrophosphorescent light-emitting diodes

We demonstrate high efficiency polymer electrophosphorescent light-emitting diodes based on a new iridium complex tris{diphenyl-(4-pyridin-2-yl-phenyl)- amine}iridium (III) (Ir(dpppa)₃) doped into a poly (N-vinyl carbazole) (PVK) host. Electron transporting 1,3,5-tris(2-N- phenylbenzimidazolyl) benzene (TPBI) and hole transporting N,N-bis-(1-naphthyl)- N,N′-diphenyl-1,1′-biphenyl-4, 4′-diamine (NPB) were doped simultaneously into the host to improve the transport balance of the charge carriers and avoid the accumulation of the space charges caused by unbalanced charge transport and direct carrier trapping on Ir(dpppa)₃. The effect of the TPBI and NPB concentrations was examined. By optimizing the concentrations of the TPBI and NPB in the blend, the device showed a current efficiency as high as 25.2 cd A^-1 at a current density of 0.85 mA cm^-2.