There have been dozens of reports of MR-TADF emitters containing sulfur and/or selenium atoms, included with the objective to increase RISC. However, the impressively high EQEmax and suppressed efficiency roll-off of the devices with all of these emitters still depended on exploiting a HF mechanism, which requires the assistance of TADF sensitizers or TADF hosts to facilitate triplet exciton harvesting (Figure , Table ). In other words, the presence of the chalcogen in these examples had only a limited effectiveness. In the case of this work, when 10 wt% of 5CzBN was incorporated within the EML as a TADF sensitizer for tDPABT1B and tDPABT2B, the EQEmax values improved to 28.0 and 28.6%, and EQE1000 values to 17.1 and 21.5%, respectively, in the HF devices with tDPABT1B and tDPABT2B. The OLED with the emitter tCzBT2B demonstrates comparable EQEmax and EQE1000