The combination of a donor-acceptor thermally activated delayed fluorescence moiety (TADF) and a multiresonant (MR-TADF) emitting core results in outstanding electroluminescence performance

Here we demonstrate the utility and potential of an emitter design consisting of a narrowband-emitting multiresonant thermally activated delayed fluorescent (MR-TADF) core that is decorated by a suitably higher energy donor-acceptor TADF moiety. Not only does this D-A TADF group offer additional channels for triplet exciton harvesting and confers faster reverse intersystem crossing kinetics but it also acts as a steric shield, insulating the emissive MR-TADF core from aggregation-caused quenching. Two emitters, DtCzBN-CNBT1 and DtCzBN-CNBT2, demonstrate enhanced photophysical properties leading to outstanding performance of the organic light-emitting diodes (OLEDs). DtCzBN-CNBT2, containing a D-A TADF moiety, has a faster kRISC (1.1 × 105 s-1) and higher photoluminescence quantum yield (ΦPL: 97%) compared to DtCzBN-CNBT1 (0.2 × 105 s-1, ΦPL: 90%), which contains a D-A moiety that itself is not TADF. The sensitizer-free OLEDs with DtCzBN-CNBT2 achieve a record-high maximum external quantum efficiency (EQEmax) of 40.2% and showed milder efficiency roll off (EQE1000 of 20.7%) compared to the DtCzBN-CNBT1-based devices (EQEmax of 37.1% and EQE1000 of 11.9%).