Cyclohexane-cored dendritic host materials with high triplet energy for efficient solution-processed blue thermally activated delayed fluorescence OLEDs

Two dendritic host materials (CH-2D1 and CH-2D2) are developed by using non-conjugated cyclohexane core and two first/second generation carbazole dendrons, which show excellent solubility in organic solvents, high thermal stability and high triplet energy (E-T) of 2.78-2.84 eV, making them suitable for fabrication of solution-processed blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Compared to CH-2D1 with the first-generation carbazole dendron which shows low-lying highest occupied molecular orbital (HOMO) energy level of -5.48 eV, CH-2D2 with the second-generation carbazole dendrons exhibits higher HOMO level of -5.37 eV, which is more favourable for hole injection from the anode to the emissive layers. Consequently, solution-processed blue TADF OLEDs utilizing CH-2D2 as host show promising device performance with a low turn-on voltage of 3.4 V, maximum external quantum efficiency of 17.8%, maximum luminous efficiency of 41.3 cd A(-1) and power efficiency of 33.9 lm W-1, which can compare with the most efficient solution-processed blue TADF OLEDs based on small-molecule and polymer hosts. These results indicate that dendritic host materials with well-defined chemical structure and good solubility are an attractive approach-beyond the soluble small-molecule hosts and polymer hosts-for the development of efficient solution-processed TADF OLEDs.