Novel yellow thermally activated delayed fluorescence emitters for highly efficient full-TADF WOLEDs with low driving voltages and remarkable color stability

White organic light-emitting diodes (WOLEDs) based on all thermally activated delayed fluorescence (TADF) emitters are especially attractive due to the merits of high efficiency and low cost. Novel TADF emitters (TFM-QP and CN-QP) were developed by selecting 6-(trifluoromethyl)quinoxaline or 6-(cyano) quinoxaline as the electron acceptor and phenoxazine as the electron donor. Aggregation induced emission is detected. Small singlet and triplet energy splitting values of 0.03-0.04 eV and long fluorescence lifetimes of 1.6-5.0 mu s confirm their TADF nature. The chromaticity of monochromic OLEDs with TFM-QP and CN-QP as doped emitters was adjustable from yellow to orange-red by varying the doping concentration, and the yellow OLEDs exhibit external quantum efficiencies (eta(ext)) of 14.4% and 9.7% at a low doping level. Full-TADF WOLEDs were fabricated using TFM-QP or CN-QP in combination with the sky-blue TADF emitter DMAC-DPS. The single-emitting-layer doped warm-white OLED (CN-QP: DMAC-DPS) exhibits excellent performance with a low turn-on voltage of 2.8 V, a stable color rending index (CRI) of 72, and high efficiencies of 48.22 cd A(-1), 50.47 lm W-1, and 20.16%, which should be the highest efficiency records ever reported for full-TADF warm-white OLEDs so far. The non-doped full-TADF WOLED with an emitting layer structure of DMAC-DPS/TFM-QP/DMAC-DPS achieves a high CRI of 86 and a moderate eta(ext) of 8.7%.