tDPA-DtCzB is a sky-blue MR-TADF emitter with high thermal stability and alleviated efficiency roll-off. tDPA-DtCzB consists of an indolo[3,2,1-de]indolo[3',2',1':8,1][1,4]benzazaborino[2,3,4-kl]phenazaborine (CzBN) core with peripheral tert-butyl groups, and a di(tert-butylphenyl)amine attached to the CzBN core opposite to the boron atom. The sterically hindered groups help to reduce the contact between neighbouring molecules and the formation of triplet excitons.
OLED based on tDPA-DtCzB as the emitter exhibits a narrowband sky-blue emission with the full-width at half-maximum (FWHM) of 29 nm, the maximum external quantum efficiency (EQE) of 31.0%, and a high EQEmax of 23.3% at the practical high luminance of 1000 cd m−2.