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

Abstract

White organic light emitting diodes harvesting triplet excitons from the fluorescent blue emitter $N,N^{\prime }$ -di-1-naphthalenyl-$N,N^{\prime }$ -diphenyl-[$1,1^{\prime }:4^{\prime },1^{″}:4^{″},1^{‴}$ -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 $49.3\mathrm{lm}{\mathrm{W}}^{-1}$ total external power efficiency (24.1% quantum efficiency) at a luminance of $1000\mathrm{cd}{\mathrm{m}}^{-2}$ [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 $40.7\mathrm{lm}{\mathrm{W}}^{-1}$ , 20.3%.