Thermally activated delayed fluorescence dendrimers achieving 20% external quantum efficiency for solution-processed OLEDs

Two multi-carbazole-encapsulated TADF dendrimers were obtained by coupling tercarbazole (tBuTCz or MeOTCz) and di(pyridin-3-yl)methanone (DPyM) units. Both tBuTCz-DPyM and MeOTCz-DPyM show small singlet-triplet energy gap (Delta E-ST) values (0.01 vs. 0.02 eV) and high photoluminescence quantum yield (PLQY) values (66.2 vs. 55.0%). High-performance solution-processed OLEDs based on tBuTCz-DPyM and MeOTCz-DPyM as the emissive layer were fabricated. The tBuTCz-DPyM-based solution-processed device exhibited a maximum current efficiency (CEmax) of 52.6 cd A(-1), a maximum external quantum efficiency (EQE(max)) of 20.4% and a maximum luminance (L-max) of 6165 cd m(-2) with a low turn-on voltage of 3.2 V. The MeOTCz-DPyM-based solution-processed device also showed an efficient performance with a CEmax of 27.0 cd A(-1), an EQE(max) of 9.2%, an L-max of 8169 cd m(-2) and a low turn-on voltage of 3.4 V. The tBuTCz-DPyM-based device (I) and the MeOTCz-DPyM-based device (II) show Commission internationale de l'eclairage (CIE) coordinates of (0.25, 0.48) and (0.37, 0.54), respectively. Both tBuTCz-DPyM and MeOTCz-DPyM demonstrate a high performance among solution-processed OLEDs with TADF dendrimers.