Thermally activated delayed fluorescence sensitizer for D–A–A type emitters with orange-red light emission†
Red thermally activated delayed fluorescence (TADF) emitters with high efficiency still remain a difficulty in the field of organic light-emitting diodes (OLEDs). The key issue lies in the contradiction between red-shifting emission spectra and retaining high photoluminescence quantum yields (PLQYs). To tackle this problem, TADF-assisted fluorescent OLEDs (TAF-OLEDs) are one promising method. In this work, two charge-transfer (CT) fluorescent emitters were developed based on the D–A–A design strategy (TPA-BT-CN and ACR-BT-CN). By increasing the rigidity of the donor moiety, ACR-BT-CN shows a higher PLQY (over 80%) than that of TPA-BT-CN (∼70%). Within expectation, when utilizing TPA-BT-CN as end emitters and 4CzIPN as the sensitizer, a high EQE of approximately 10% is achieved for 0.5 wt% and 1.0 wt% based devices. Benefiting from the increased rigidity, a superior EQE of around 16% with an emission peak at 595 nm is also achieved. Furthermore, suppressed efficiency roll-off is also observed for these low-doping devices.