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

Abstract

We demonstrate a white stacked organic light-emitting device (WSOLED) employing the blue fluorescent emitter, 4,$4^{\prime }$ -bis(9-ethyl-3-carbazovinylene)-1,$1^{\prime }$ -biphenyl, and the green and red phosphorescent emitters, $fac$ -tris(2-phenylpyridinato-$N,C^{2^{\prime }}$ ) iridium (III) and iridium (III) bis(2-phenyl quinolyl-$N,C^{2^{\prime }}$ ) acetylacetonate, respectively. The charge generation region consists of a Li-doped electron transport layer and a highly transparent $\mathrm{Mo}{\mathrm{O}}_x$ 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 ${\eta }_{\mathrm{ext}}=23\%\pm 2\%$ at a current density of $J=1\mathrm{mA}∕{\mathrm{cm}}^2$ and ${\eta }_p=14\pm 1\mathrm{lm}∕\mathrm{W}$ at $J=0.17\mathrm{mA}∕{\mathrm{cm}}^2$ , 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 ${\eta }_{\mathrm{ext},\mathrm{tot}}=57\%\pm 6\%$ and ${\eta }_{p,\mathrm{tot}}=22\pm 2\mathrm{lm}∕\mathrm{W}$ , respectively, at a luminance of $1000\mathrm{cd}∕{\mathrm{m}}^2$ , 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 OLED is potentially useful for solid state lighting applications.