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

• Highly efficient green OLEDs with delayed fluorescence are fabricated.
• This host material shows a high glass transition temperature with a Tg = 110 °C and a high triplet energy of 3.02 eV.
• When doped with the TADF emitter 4CzIPN, efficiencies of over 26% EQE and 81 cd/A were achieved.
• These are among the most efficient TADF OLEDs produced.

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.

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