High efficiency deep-blue emission is essential to realize energy-saving, high-quality display and lighting applications. We demonstrate here a deep-blue organic light emitting diode using a novel carbazole based fluorescent emitter 7-[4-(diphenylamino)phenyl]-9-(2-ethylhexyl)-9Hcarbazole-2-carbonitrile (JV234). The solution processed resultant device shows a maximum luminance above 1,750 cd m %2 and CIE coordinates ð0:15; 0:06Þ with a 1.3 lm W %1 power efficiency, 2.0 cd A %1 current

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... , and 4.1% external quantum efficiency at 100 cd m %2 . The resulting deep-blue emission enables a greater than 100% color saturation. The high efficiency may be attributed to the effective host-to-guest energy transfer, suitable device architecture facilitating balanced carrier injection and low doping concentration preventing efficiency roll-off caused by concentration quenching.