High-efficiency top-emissive white-light-emitting organic electrophosphorescent devices

We demonstrate an efficient, top-emissive, white-light-emitting organic device (WOLED) employing the phosphorescent emitters, tris-(1-(4,6-difluorophenyl)pyridinato,$N$ ,$C{2}^{\prime }$ )iridium(III) and iridium(III) bis(2-phenyl quinolyl-$N$ ,$C{2}^{\prime }$ )acetylacetonate combining a sputtered Ni anode and an ITO cathode. The electron transport layer is doped with Li for efficient electron injection from the cathode, thereby also avoiding strong microcavity effects. The operating voltage is substantially reduced compared with a top-emissive device with an undoped electron transport layer. Peak external quantum and power efficiencies of $10.5\pm 1.0\%$ and $9.8\pm 1.0\mathrm{lm}∕\mathrm{W}$ are achieved at current densities of 1.6 and $1.0\mathrm{mA}∕{\mathrm{cm}}^2$ , respectively. The emission is characterized by Commission Internationale de L’Eclairage coordinates of ($x=0.42$ , $y=0.39$ ). The top-emissive device, useful for generating full color images when combined with color filters or for display backlights, exhibits characteristics competitive with those of a bottom-emission WOLED using the same multilayer structure.