Conventional fluorescence-based organic light-emitting diodes (OLEDs) have attracted wide interest due to their long operational lifetime, high color purity, low efficiency roll-off and potential to be manufactured at low cost in the applications of next-generation full-color display and solid state lighting. However, the external quantum efficiency (EQE) of fluorescent OLEDs is limited to 5% due to the inability to use the generated triplet excitons. Here, we report a blue fluorescent OLED that realizes an EQE as high as 14.1% by using a thermally activated delayed fluorescent (TADF) material as an assistant host in the emitting layer, which permits the efficient energy transfer of all generated excitons to the blue fluorescent dopant. Furthermore, color-stable hybrid warm-white OLEDs with improved lifetime also have been obtained. The maximum forward-viewing power efficiency (PE), current efficiency (CE), and EQE are as high as 68.5 lm W−1, 56.7 cd A−1 and 20.1%, respectively, and the T50 lifetime at L0 = 1000 cd m−2 reaches 1657 h. The achievement of these results fully exhibits the effectiveness of the TADF material as the assistant host to fabricate high efficiency and long lifetime fluorescent OLEDs.
