Stacked white organic light-emitting devices based on a combination of fluorescent and phosphorescent emitters

We demonstrate a white stacked organic light-emitting device (WSOLED) employing the blue fluorescent emitter, 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl, and the green and red phosphorescent emitters, fac-tris(2-phenylpyridinato-N, C ^2′) iridium (III) and iridium (III) bis(2-phenyl quinolyl-N, C ^2′) acetylacetonate, respectively. The charge generation region consists of a Li-doped electron transport layer and a highly transparent MoO _x thin film. For a two-element white SOLED (2-WSOLED), the combination of red and green phosphors with a blue fluorophore yields maximum external quantum and power efficiencies of η _ext=23% ±2% at a current density of J=1 mA/cm ² and η _p=14±1 lm/W at J=0.17 mA/cm ², respectively. Due to the low optical and electrical losses of the charge generation layer, the efficiencies scale approximately linearly with the number of independent emissive elements in the WSOLED. Hence, for a 3-WSOLED, the total external and power efficiencies estimated for operation of the device in a light fixture are η _ext,tot =57% ±6% and η _p,tot=22±2 lm/W, respectively, at a luminance of 1000 cd/m ², with Commission Internationale de L'Eclairage chromaticity coordinates of (x=0.38, y=0.44), and a color rendering index of 82. The high-efficiency, high brightness, stacked white PLED is potentially useful for solid state lighting applications.