BN-CP1 is a highly efficient MR-TADF green emitter with a maximum external quantum efficiency (EQEmax) up to 40.0% and full width at half maximum (FWHM) of 25 nm. BN-CP1 has an indolo[3,2,1-de]indolo[3',2',1':8,1][1,4]benzazaborino[2,3,4-kl]phenazaborine (Cz-BN) core with four peripheral bulky tert-butyl groups, and 2,3-carbazolylphenyl attached to the CzBN core opposite to the boron atom. The unique three-dimensional geometry and steric effect created by the tert-butyl and neighbouring two carbazolyl groups are favorable for suppressing chromophore interactions such as the aggregation-caused-quenching (ACQ). This is manifested by the minor change of FWHM from 25 to 26 nm upon increasing the doping concentration from 1 to 30 wt.% in DMIC-TRZ film.
BN-CP1 can also be considered as a derivative of DtBuCzB. OLED device based on BN-CP1 as the emitter and DMIC-TRZ as the host demonstrates an unchanged electroluminescence λem of 496 nm and FWHM of 25 nm, and a smaller decrease of EQEmax from 40.0 to 33.3% as the doping concentration increased from 5 to 30 wt.%. BN-CP1 is a good example of doping-insensitive MR-TADF material with great electroluminescence efficiency and color purity.