High-Efficiency White Organic Light-Emitting Diodes Based on Phosphorescent Iridium Complex and 4,4'-Bis[N-1-napthyl-N-phenyl-amino]biphenyl Emitters

High-efficiency white organic light-emitting devices (WOLEDs) based on phosphorescent dye bis[2-(4-tert-butylphenyl)benzothiazolato-N,C2']iridium (acetylacetonate) [(t-bt)2Ir(acac)] doped 4,4'-bis(carbazol-9-yl) biphenyl (CBP) as a yellow-emitting layer together with blue fluorescent emitter and hole-transporting material 4,4'-bis[N-1-napthyl-N-phenyl-amino]biphenyl (NPB) were fabricated. In those devices with a simple structure, 2,9-dimethyl,-4,7-diaphenyl,1,10-phenanthroline (BCP) and tris(8-quinolinolato) aluminum (Alq) were used as hole-blocking and electron-transporting layers, respectively. The purity of white light can be adjusted by doping concentration and bias voltage. The device shows a maximum luminance of 7580 cd/m2 with a luminance efficiency of 4.32 cd/A and Commission International De L'Eclairage (CIE) coordinates of (0.319,0.342) at 13.5 V. A maximum luminance efficiency of 10.2 cd/A at a current density of 0.026 mA/cm2 was achieved.