Light-blue thermally activated delayed fluorescent emitters realizing a high external quantum efficiency of 25% and unprecedented low drive voltages in OLEDs

Thermally activated delayed fluorescent (TADF) emitters are one of the most promising candidates for low-cost and high efficiency organic light-emitting devices (OLEDs) to realize an internal quantum efficiency of unity. However, the power efficiency (eta(p)), which is inversely related to the drive voltage, is significantly lower than that of the phosphorescent counterparts, especially for blue devices. Here, we developed a series of TADF emitters, 2-functionalized-4,6-bis[4-(9,9-dimethyl-9,10-dihydroacridine) phenyl] pyrimidine called Ac-RPM. We introduced a phenylacridine moiety into the 4,6-position of the pyrimidine core to induce a twisted structure leading to a high photoluminescence quantum yield of similar to 80%, and a small singlet and triplet excited energy difference of <0.20 eV. The optimized device realized an eta(p) of 62 lm W-1, a high external quantum efficiency of 25%, light-blue emissions with the Commission Internationale de l'Eclairage chromaticity coordinates of (0.19, 0.37) and a low turn-on voltage of <3.0 V.