Highly efficient Organic Light-Emitting Diodes from thermally activated delayed fluorescence using a sulfone–carbazole host material

Organic Light-Emitting Diodes (OLEDs) using the thermally activated delayed fluorescence (TADF) emitter (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) are demonstrated using a novel ambipolar host 3,5-di(carbazol-9-yl)-1-phenylsulfonylbenzene (mCPSOB). When doped in a 5 wt.% concentration, OLEDs with EL efficiency values of more than 81 cd/A for current efficacy and 26.5% for external quantum efficiency are reported. These devices exhibit a low turn-on voltage of 3.2 V at 10 cd/m2, as well as reduced efficiency roll-off at high current densities. To the best of our knowledge, these are among the highest ever reported efficiencies for TADF OLEDs, and are even comparable to the highest reported efficiencies for phosphorescent OLEDs.