Peripheral decoration of multi-resonance TADF emitter for narrowband blue OLEDs

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with high efficiency and narrowband blue emission are highly demanded for high-quality displays. In this study, two MR-TADF emitters, namely CzBN-tDPA and CzBN-mCP, were designed by decorating the well-known emitter of CzBN with different diarylamino moieties. This peripheral decoration strategy successfully results in blue emission with peaks at 465 and 464 nm, narrow full-width at half maximum (FWHM) values of 23 and 21 nm for CzBN-tDPA and CzBN-mCP in toluene solution, respectively. The new emitters exhibit faster rate constants of reverse intersystem crossing and higher photoluminescence quantum yields, compared to the parent molecule. As a result, organic lightemitting diodes based on CzBN-tDPA and CzBN-mCP exhibit narrowband blue emission with maximum external quantum efficiencies (EQEmaxs) of nearly 20% and low efficiency roll-offs. More importantly, decent EQEmax up to 30.6% could be realized in hyperfluorescence devices adopting these two new emitters.