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,C2′) iridium (III) and iridium (III) bis(2-phenyl quinolyl-N,C2′) acetylacetonate, respectively. The charge generation region consists of a Li-doped electron transport layer and a highly transparent MoOx 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 ηext=23%±2% at a current density of J=1mA∕cm2 and ηp=14±1lm∕W at J=0.17mA∕cm2, 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 ηext,tot=57%±6% and ηp,tot=22±2lm∕W, respectively, at a luminance of 1000cd∕m2, 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 OLED is potentially useful for solid state lighting applications.