Reduced efficiency roll-off in high-efficiency hybrid white organic light-emitting diodes

White organic light emitting diodes harvesting triplet excitons from the fluorescent blue emitter N,N(')-di-1-naphthalenyl-N,N(')-diphenyl-[1,1':4',1 '':4 '',1'"-quaterphenyl]-4,4'-diamine (4P-NPD) are presented. Direct doping of the phosphorescent orange iridium(III)bis(2-methyldibenzo-[f,h]quinoxaline)(acetylacetonate) into 4P-NPD results in a strongly reduced efficiency roll-off as compared to separate emission layers, and yields 49.3 lm W(-1) total external power efficiency (24.1% quantum efficiency) at a luminance of 1000 cd m(-2) [CIE 1931 chromaticity coordinates (0.49,0.41)], measured in an integrating sphere. Introduction of an exciton balancing interlayer improves the chromaticity (0.43,0.43) toward the CIE illuminant A warm white point and keeps a high efficiency of 40.7 lm W(-1), 20.3%. (c) 2008 American Institute of Physics.