Although the strategy of decorating MR-TADF cores with bulky groups can effective supress the ACQ, the slow RISC rate (kRISC) of most MR-TADF results in a build-up of triplet excitons at high current density, leading ultimately to severe efficiency roll-off due to exciton annihilation processes such as triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA). The most successful solution to address efficiency roll-off to date has been to decouple exciton harvesting and emission within a HF-OLED wherein the assistant dopant harvests the excitons before transferring their energy to the terminal MR-TADF emitter by FRET. To date, there are only a few examples of solution-processed MR-TADF OLEDs and those documenting HF-OLEDs are even more limited. This is likely due to the general poor solubility of the MR-TADF emitter, and for HF-OLEDs, the difficulty in obtaining homogenous films with high FRET efficiency in ternary solution-processed blends. In this work, we propose an emitter design that combines within a single emitter structure a moiety that acts as a TADF sensitizer to efficiently harvest excitons that then get transferred by Förster resonance energy transfer (FRET) to an MR-TADF moiety responsible for the narrowband emission. Compound DtBuCzB was selected as the MR-TADF emitting core thanks to its fast radiative rate (kr ~ 10 8 s -1 ), and narrowband emission (λPL = 483 nm, FWHM = 23 nm in toluene solution 10 -5 M), while this moiety was sandwiched between to TADF dendrimers, 2GtBuCzCO2H, bearing second-generation tert-butyl carbazole donor dendrons linked to a benzoate acceptor. These dendrimer groups in 2GtBuCzCO2HDCzB act to shield the MR-TADF core from intermolecular interactions (Figure ). For comparison, we also designed tBuCzCO2HDCzB, which only contains tert-butyl carbazoles that are less effective at encapsulating the MR-TADF emissive core. In 30 wt% doped film in mCP, 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB possess similarly high FPL of 98 and 94%, ΔEST of 0.15 and 0.14 eV, τd of 143 and 102 µs, and kRISC of 1.23×10 4 and 2.37×10 4 s -1 . The combination of the ortho-carbazole-based donors and the para cyano group on the pendant phenyl ring of the MR-TADF core DtBuCzB endows both emitters simultaneously with a strong resistance to ACQ and more efficiency exciton harvesting, which translates to solutionprocessed devices that show both higher EQEmax and lower efficiency roll-off. Compared to the tert-butyl carbazole-substituted tBuCzCO2HDCzB, 2GtBuCzCO2HDCzB exhibits improved resistance to aggregation and ACQ as well as a resistance the bimolecular exciton quenching processes in the SP-OLEDs. The SP-OLEDs with 30 wt% 2GtBuCzCO2HDCzB and tBuCzCO2HDCzB in the EML showed high EQEmax of 27.9 and 22.0% and low efficiency roll-off, with EQE5000 of 22.3 and 16.3%, respectively. Moreover, the EQEmax of the host-free SP-OLEDs with 2GtBuCzCO2HDCzB remained high at 24.0% while the efficiency roll-off remained low (EQE1000 of 20.2%), while the host-free devices with tBuCzCO2HDCzB performed much worse, reflected in the much lower EQEmax of 11.4%.