Influence of Dopant Concentration on Electroluminescent Performance of Organic White-Light-Emitting Device with Double-Emissive-Layered Structure

A novel phosphorescent organic white-light-emitting device (WOLED) with configuration of ITO/NPB/CBP:TBPe:rubrene/Zn(BTZ)2:Ir(piq)2(acac)/Zn(BTZ)2/Mg:Ag is fabricated successfully, where the phosphorescent dye bis (1-(phenyl)isoquinoline) iridium (III) acetylanetonate (Ir(piq)2(acac)) doped into bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTZ)2) (greenish-blue emitting material with electron transport character) as the red emitting layer, and fluorescent dye 2,5,8,11-tetra-tertbutylperylene (TBPe) and 5,6,11,12-tetraphenyl-naphthacene (rubrene) together doped into 4,4'-N,N'-dicarbazole-biphenyl (CBP) (ambipolar conductivity material) as the blue-orange emitting layer, respectively. The two emitting layers are sandwiched between the hole-transport layer N,N'-biphenyl-N, N'-bis (1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) and electron-transport layer (Zn(BTZ)2). The optimum device turns on at the driving voltage of 4.5 V. A maximum external quantum efficiency of 1.53% and brightness 15000 cd/m2 are presented. The best point of the Commission Internationale de l'Eclairage (CIE) coordinates locates at (0.335, 0.338) at about 13 V. Moreover, we also discuss how to achieve the bright pure white light through optimizing the doping concentration of each dye from the viewpoint of energy transfer process.