Electroluminescent characteristics of white organic light-emitting diodes using two different red dopants

Authors have demonstrated highly efficient white organic light-emitting diodes (WOLEDs) using the same blue emitter, 1,4-bis[2-(7-N-diphenyamino-2-(9,9-diethyl-9H-fluoren-2-yl)) vinyl] benzene (DAF-ph), and the different red emitters, bis(5-isobutyryl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) ((Ibppy)2Ir(acac)) and bis(5-acetyl-2-phenylpyridinato-C,N) iridium(III) (acetylacetonate) ((acppy)2Ir(acac)). Although the red emitters had the same highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), they showed the different electrical and optical characteristics due to the difference of stearic hindrance. Two devices showed the maximum luminance of 21,600 and 30,500 cd/m2 at 14 V, maximum luminous efficiency of 30.2 and 38.0 cd/A at 0.004 and 0.005 mA/cm2, and CIEx,y coordinates of (x=0.37, y=0.43) and (x=0.33, y=0.40) at 10 V, respectively.