Color-stable all-fluorescent WOLEDs with single bipolar host based on a red TADF emitter

摘要

High color rendering index and color-stable all-fluorescent white organic light-emitting devices (WOLEDs) with a red thermally activated delayed fluorescence(TADF) emitter using 2,3,5,6-tetrakis(3,6-diphenylcarbazol-9-yl)-1,4-dicyanobenzene (4CzTPN-Ph) and a blue fluorescent emitter (DSA-Ph) doped in a bipolar host emitter were fabricated. Extended exciton recombination zone by a bipolar host emitter contributes to balance the distribution of carriers in the emitting layer. The device exhibits high color stable white emission with a slight Commission International de l'Eclairage (CIE) coordinates variation of (0.002, 0.001) at a luminance ranging from 500 cd m-2 to 5000 cd m-2, the CIE coordinate of (0.40, 0.38) and the CRI up to 74. These results indicate that the application of a single bipolar host, a spacer-free layer structure, and a TADF emitter has a significant effect on achieving spectrally stable emission, improving the color rendering index, and reducing the efficiency roll-off of the fluorescent WOLEDs.