x/y CIE coordinates of 0.28/0.35 and high EQE of 15.5%. Similarly, another HF-WOLED developed using a TADF emitter T23 and orange-emitting rubrene (F9) without any host, reached EQEs of 7.48%. In addition, stable EL spectra were recorded with the change of the x/y CIE coordinates of 0.36/0.41 to 0.36/0.43 with increase in voltage from 5 V to 8 V. Friend and coworkers reported a HF-WOLED by using a skyblue TADF emitter T24, complemented by yellow and red emitting fluorescence emitters F5 and F1, the device resulted in a high EQE of 21.8% with x/y CIE coordinates of 0.43/0.45. Very recently, the Xu group reported an ultra-thin bilayer concept for the design of HF-WOLED, where a emissive layer contains an ultrathin layer of blue fluorescence emitter (F3), and a layer of TADF emitter (T25 or T26) doped with a yellow fluorescence emitter (F5). The efficiency of these HF-WOLEDs is highly sensitive to the thickness of the layers. At the thinness of 0.1nm of blue emitter layer, the device exhibits dual band EL spectra with x/y CIE coordinates of 0.40/0.50. The maximum EQE values of 20.9%, and 11.8 % are reported for the devices using TADF emitters T25 and T26, respectively. Similarly, the Tang group recently reported a HF-WOLED using a yellow emitter F5 , blue emitter F11 and a TADF emitter, T6 with a pure hydrocarbon host, SF4-TPE. They witnessed with an increase in thickness of the blue layer, the EL intensity becomes stronger and the HF-WOLED constructed using 10 nm thickness of the blue layer exhibited maximum EQE of 17 Interestingly, these efficiencies of HF-OLEDs are much higher compared to reported fluorescence OLEDs.