The HF-OLED fabricated with 30 wt% TADF sensitizer T17 and 1 wt% MR-TADF emitter MR-T1, resulted in a maximum EQE of 20.6% with a narrow FWHM of 21 nm that has x/y CIE chromaticity coordinates of 0.140/0.195. In parallel, many researchers exploited B, N doped MR-TADF terminal emitters in HF-OLEDs to achieve narrow emission with high efficiencies and high color purity. Kwon group reported a modified MR-TADF emitter (MR-T2) by attaching the tert-butyl group to the MR-T1 core. As mentioned earlier, incorporating bulky groups into the backbone of the terminal emitter can effectively inhibit the DET process and increase PL. In thin film, MR-T2 displayed a PL of 91.9%. This increase in PL compared to MRT1 is due to the addition of the tert-butyl group. MR-T2 showed a short delayed lifetime of 2.93 µs, and kRISC of 2.54 × 10 5 s -1 . Therefore, they have selected a suitable TADF emitter, T18 to sensitize the blue emission of the MR-TADF emitter, MR-T2. The thin film obtained with 30 wt.% T18 and 1% of MR-T2 has a PL of 97.3% and a kFRET of about 7.77× 10 7 s -1 . This indicates efficient energy transfer from T18 to MR-T2. Therefore, the blue HF-OLED fabricated with the MR-T2:T18 combination exhibits a maximum EQE of 40.7% along with a narrow FWHM of 19 nm and x/y CIE chromaticity coordinates of 0.12/0.15. Zysman-Colman group reported a different B, N doped MR-TADF emitter, MR-T3.