High-Efficiency Red-Fluorescent Organic Light-Emitting Diodes with Excellent Color Purity

Thermally activated delayed fluorescence (TADF)-sensitized fluorescent OLEDs are promising for next-generation OLEDs. However, the performance of these OLEDs with deviated CIE coordinates from the fluorescent emitters is still unsatisfactory due to the insufficient Förster resonance energy transfer (FRET). Here we report a rational strategy to construct a highly efficient TADF-sensitized fluorescent OLED system by the dedicated selection of the host and the TADF sensitizer. Benefiting from the efficient energy-transfer process from TXO-TPA to DBP, the TADF-sensitized fluorescent OLEDs exhibited a maximum EQE of 16.9%. Furthermore, a new factor, the sensitization efficiency (SE), was first introduced to quantitatively evaluate the contribution of the fluorescent emission. A high SE up to 96.4% can be achieved for the reported OLEDs with CIE coordinates of (0.65, 0.35), which are very close to the standard red CIE coordinates of (0.67, 0.33). Our discussion will aid in the design and evaluation of more efficient TADF-sensitized fluorescent OLEDs.