to 48% efficiency roll-off for the device with tCzBT1B at same luminance (EQE1000: 18.0%). The TADF-sensitized hyperfluorescent (HF) devices, with 10 wt% 5CzBN as the assistant dopant and using tDPABT1B or tDPABT2B, showed sky-blue emission with CIE coordinates of (0.13, 0.33) and (0.13, 0.30), respectively. Their EQE vs luminance curves also showed a similar trend, with EQEmax of 28.0% and 28.6%, and EQE1000 of 17.1% (39% efficiency loss) and 21.5% (25% efficiency loss) for the devices with tDPABT1B or tDPABT2B, respectively. This work showcases the importance of the placement of the heavy atom in accelerating RISC, leading to higher-performance devices.