In contrast, Lee group reported a HF-OLED showing improved EQEs, which contain a deep blue TADF emitter (T8) and fluorescence emitter (F3). At 50 wt.% doping concentration of T8 and 0.1 wt.% doping concentration of F3, a deep blue HF-OLED was fabricated with host DPEPO (Table ). This resulted in an improved EQE reaching a value of 18.1%. These studies suggest that the choice of the T8:F3 couple is better than the T4:F3 couple for blue HF-OLED (Figs. and). Further studies revealed that a blue HF-OLED constructed using a T8:F3 couple without a host exhibits EQE of 15.4 %. As the next steps, another TADF emitter T9 was used to sensitize the blue emission of F3. Similar to the previous works, a solution-processed efficient blue HF-OLEDs was prepared, reaching an EQE of 18.8 % using a bulkier host DPOBBPE (Table ). These findings revealed that the nature of the host plays a vital role f in the device's performance by controlling Dexter energy transfer; the bulkier the host, the lesser will be the Dexter energy transfer. Kwon group recently developed two more blue-emitting TADF emitters, T1 and T2 (Fig. ). Both emit deep blue emissions and exhibit high PL. HF-OLEDs were fabricated using F1 as a dopant with host DBFPO. The blue HF-OLEDs achieved using the T1:F1 and T2:F2 couple exhibit impressive EQE of 38.8% and 37.3%, respectively. In addition, the EL spectra of the both blue HF-OLEDs featured a FWHM of 19 nm. Very recently Kwon group reported one blue HF-OLED using T10 as quadrupolar donor-acceptor-donor type TADF emitter and F1 as a fluorescence emitter in DBFPO host (Fig. ) . The HF-OLED device fabricated with this combination exhibits high EQEs of 43.9% of with x/y CIE chromaticity coordinates of 0.12/0.16. This significant increase was attributed to the successful control of the DET process through efficient KRISC and shielded LUMO in T10. In addition, the HF-OLED constructed using the T10:F1 couple displays an EL peak maximum at 473 nm with a narrow FWHM of 21 nm. These investigations suggest an efficient HF-OLED could be developed by the proper selection of host, TADF emitter, and fluorescence terminal emitter.