Highly efficient top-emitting green phosphorescent OLEDs with a narrow band and slow efficiency roll-off for high-definition displays

New bipolar hosts are used to fabricate green-phosphorescent OLEDs, realizing a narrow full width at half maximum of 28 nm, high efficiencies of 183.1 cd A −1 and 247.3 lm W −1 , and slow efficiency roll-off with 132.2 cd A −1 at 66 000 cd m −2 .