Owing to their exciting properties, these compounds were employed as emitters in OLED devices, and to assess improvements in efficiency roll-off, they were also investigated as terminal emitters in hyperfluorescence (HF) OLEDs, which combine a narrowband emitter as terminal dopant with a co-deposited TADF emitter acting as an assistant dopant in a host matrix. Although MR-TADF OLEDs have achieved extremely high EQEmax, an issue generally encountered is the severe efficiency roll-off that is mainly caused by quenching mechanisms such as singlet-triplet annihilation (STA) and triplet-triplet annihilation (TTA) due to the accumulation of triplet excitons as a result of their typically slow reverse intersystem-crossing rate (kRISC). Therefore, a potential solution to circumvent this issue is to use MR-TADF compounds in combination with an efficient exciton harvesting assistant dopant in a HF device. In these devices, exciton harvesting is managed by the donor-acceptor TADF assistant dopant and these excitons are transferred to the terminal MR-TADF emitter via a Förster resonant energy transfer (FRET) mechanism. Emission from the terminal emitter then occurs, benefiting from the typically fast radiative decay and narrowband emission of the MR-TADF compound. To ensure efficient FRET, there must be an effective overlap between the emission spectrum of the assistant dopant and the absorption spectrum of the emitter.