Abstract: High-efficiency white organic light-emitting devices (WOLEDs) based on phosphorescent dye bis[2-(4-tert-butylphenyl)benzothiazolato-N,C^2’]iridium (acetylacetonate) [(t-bt)₂Ir (acac)] doped 4,4’-bis (carbazol-9-yl) biphenyl (CBP) as a yellow emitting layer were fabricated. The structure of the devices is indium tin oxide (ITO)/N,N’-bis-(1-naphthyl)-N,N’-biphenyl-1,1’-biphenyl-4,4’-diamine (NPB)/CBP: (t-bt)₂Ir(acac)/NPB/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/8-hydroxyquinoline aluminum(Alq₃)/Mg:Ag, and the second NPB layer fromthe anode was used as a blue fluorescent emitter and the first NPB layer was used as a hole transporting layer, the BCP and Alq₃ were used as hole blocking and electron transporting layers, respectively. The turn-on voltage of the device was 3 V with a maximumluminance of 15460 cd·m^-2 at 16.5 V and maximumluminance efficiency of 7.5 lm·W^-1 at 4 V, respectively. The Commission Internationale de I’Eclairage (CIE) coordinates located at (0.33, 0.32) remained stable at the driving voltage higher than 8 V, which is almost consistent with the optimum white CIE of (0.33, 0.33). The purity of white light could be adjusted by doping concentration. The effect of charge carrier trapping and energy transfer on the device performance were also discussed.

Key words: Organic light-emitting diodes, White light, Phosphorescence, Iridium complex, Carrier trapping, Energy transfer