In this work, to realize such a molecular design, we connected a high-energy D-A TADF moiety to the MR-TADF-emitting core DtCzBN in order to introduce multiple exciton-harvesting channels akin to conventional HF systems. Two proof-of concept emitters DtCzBN-CNBT1 and DtCzBN-CNBT2, respectively, employ two bis(benzothienocarbazol-5-yl) benzonitrile isomers (CNBT1 and CNBT2 (Figure ) as the D-A-type moieties, which are substituted onto the DtCzBN core and adopt a strongly twisted conformation. In particular, CNBT2 itself is TADF, with an associated ΔEST of 0.28 eV and a delayed lifetime (τd) of 159 µs in 15 wt% doped films in PhCzBCz, while CNBT1 has a larger ΔEST of 0.36 eV and there is no observed delayed fluorescence in the doped PhCzBCz film. Both DtCzBN-CNBT1 and DtCzBN-CNBT2 show narrowband emission peaking at lPL of ca. 500 nm. Benefiting from the auxiliary D-A TADF moiety CNBT2, DtCzBN-CNBT2 has a five-fold faster kRISC of 1.1 × 10 5 s -1 and higher ΦPL of 97% than DtCzBN-CNBT1 (kRISC of 2.0 × 10 4 s -1 , ΦPL of 90%). The sensitizerfree OLEDs with 15 wt% DtCzBN-CNBT2 in PhCzBCz host showed green emission with CIE coordinates of (0.16, 0.67) and a record-high EQEmax of 40.2%, while the EQE at 1000 cd m -2 was 20.7%. The DtCzBN-CN BT1-based device showed a comparably high EQEmax of 37.1% at CIE coordinates of (0.17, 0.66); however, the device exhibited severe efficiency roll-off, with the EQE reducing to 11.9% at 1000 cd m -2 due to the slower kRISC of the emitter. The state-of-the-art device performance using DtCzBN-CNBT2 validates the effectiveness of the emitter design, which simultaneously boost kRISC, FPL, and maintains the narrowband emission associated with MR-TADF materials.