By adopting an emitter design that thoroughly encapsulates the MR-TADF emissive core DtBuCzB within flanking donor-acceptor TADF groups, both 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB showed bright green emission that was resistant to aggregation and aggregation-caused quenching, even as neat films. We demonstrated through a combined computational and photophysical study how the donor-acceptor TADF groups act to harvest excitons and then efficiently transfer their energy by FRET to the MR-TADF core where emission occurs. The use of TADF dendrimers in 2GtBuCzCO2HDCzB results in improved suppression of concentration quenching. The SP-OLEDs with 2GtBuCzCO2HDCzB in 30 wt% mCP emitted narrowband green emission at λEL of 495 nm and FWHM of 27 nm and showed both a high EQEmax of 27.9% and a small efficiency roll-off with EQE5000 of 22.3%. Though the photophysics of tBuCzCO2HDCzB was similar to that of 2GtBuCzCO2HDCzB the EQEmax of the device with tBuCzCO2HDCzB was only 22.0% and the efficiency roll-off was larger where the EQE5000 was 16.3%. The EQEmax of the host-free SP-OLEDs with 2GtBuCzCO2HDCzB remained high at 24.0% and the efficiency roll-off was low, with EQE1000 of 20.2%, which is comparable with our previous reported tBuCz2m2pTRZ dendrimer OLED (EQEmax = 28.7%), especially at high brightness (EQE500 of 22.7%). These results demonstrate the value of this emitter design to translate into high-performance SP-OLEDs.