A hybrid white organic light-emitting diode (WOLED) with an external quantum efficiency above 20% was developed using a new blue thermally activated delayed fluorescent material, 4,6-di(9H-carbazol-9-yl)isophthalonitrile (DCzIPN), both as a blue emitter and a host for a yellow phosphorescent emitter. DCzIPN showed high quantum efficiency of 16.4% as a blue emitter and 24.9% as a host for a yellow phosphorescent emitter. The hybrid WOLEDs with the DCzIPN host based yellow emitting layer sandwiched between DCzIPN emitter based blue emitting layers exhibited high external quantum efficiency of 22.9% with a warm white color coordinate of (0.39, 0.43) and quantum efficiency of 21.0% with a cool white color coordinate of (0.31, 0.33) by managing the thickness of the yellow emitting layer.
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Cho et al. (2015) studied this question.