Multiple-resonance thermally activated delayed emitters through multiple peripheral modulation to enable efficient blue OLEDs at high doping levels

Organic light-emitting diodes (OLEDs) based on multiple resonance-thermally activated delayed fluorescence (MR-TADF) have the advantages of high exciton utilization and excellent color purity. However, the large conjugated planarity of general MR-TADF emitters makes them easily aggregate in the form of π–π stacking, resulting in aggregation-caused quenching (ACQ) and the formation of excimers, which reduce exciton utilization efficiency and color purity. To address these issues, large shielding units can be incorporated to prevent interchromophore interactions, whereas the majority of reported molecules are limited to blue-green light emissions. This work proposes a strategy of incorporating steric hindrance groups at different sites of the B/N core to suppress interactions between chromophore, contributing to blue MR-TADF emitters with high photo-luminance quantum yields (PLQYs ≥ 95%) and narrow full width at half maximum (FWHM), and importantly, great suppression of the ACQ effect. Therefore, blue OLEDs achieve high external quantum efficiencies up to 34.3% and high color purity with FWHM of about 27 nm and CIE around (0.12, 0.15), even at a high doping concentration of 20 wt%.