An electroluminescence efficiency of 30.3% for a yellow thermally activated delayed fluorescence emitter with a high horizontal emitting dipole ratio

Thermally activated delayed fluorescence (TADF) emitters with a high horizontal emitting dipole ratio (Θ_‖) remain a hot spot in the application of organic light-emitting diodes (OLEDs), which may achieve an extremely high external quantum efficiency (EQE). Herein, two yellow TADF emitters, 3,6,11-triTPA-BPQ and 3,6,12-triTPA-BPQ based on the triphenylamine (TPA) donor, have been synthesized by reasonably introducing nitrogen atoms into different positions of the acceptor core. Both emitters exhibit high horizontal emitting dipole ratios of 92% in doped organic films with photoluminescence quantum yields (Φ_PL) of 94.0% and 78.4%, respectively. Because of high Φ_PL and high light out-coupling ratio induced by high Θ_‖ for 3,6,11-triTPA-BPQ, yellow OLEDs using this emitter achieve a maximum external quantum efficiency of 30.3%, which provides a novel way to boost the efficiency of yellow TADF-OLEDs.