A Study on White Organic Light-Emitting Diodes Co-Doped with Red Fluorescent and Blue Phosphorescent Dopants

초록

White organic light-emitting diodes (WOLEDs) have drawn increasing attention due to their potential use in various applications such as solid-state lighting and backlight of liquid crystal displays and full-color OLEDs of red, green, and blue pixel. N,N'-dicabazolyl-3,5-benzene (mCP), the host material, was co-doped with Iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2']-picolinate (Flrpic), which functions not only as phosphorescent sensitizer but also blue emitter, and (2Z,2'Z)-3,3'-[4,4 ''-bis (dimethylamino)-1,1':4',1 ''-terphenyl-2',5'-diyl]bis (2-phenylacrylonitrile) (ABCV-P), which is a red fluorescent material. The fabricated device structures were as follows: (device A) Indium tin oxide (ITO)/N,N'-bis-(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/(mCP)/mCP:ABCV-P (1%)/4,7-diphenyl-1,10-phenanthroline (Bphen)/lithium quinolate (Liq)/aluminum (Al), (device B) ITO/NPB/mCP/mCP:Flrpic (8%)/Bphen/Liq/Al and (device C) ITO/NPB/mCP/mCP:Flrpic:ABCV-P (8%, 1%)/Bphen/Liq/Al, respectively. Phosphorescent Flrpic harvesting both singlet and triplet excitions not only emitted blue light but also transferred energy to fluorescent ABCV-P. The maximum luminance efficiency, external quantum efficiency, and luminance of white light device were measured to be 5.95 cd/A, 2.45% and 2500 cd/m(2), respectively. The white device gave practically white light with the Commision Internationale de l'Eclairage (CIExy) coordinate of (0.44, 0.49) which was close to warm white color (CIExy = 0.45, 0.45).

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