TDBA-DI is a MR-TADF blue emitter consisting of a tert-butyl decorated DOBNA core acceptor and a 10,15-dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole donor unit. Benefiting from the large steric hindrance between the donor and the oxygen-bridged boron acceptor, TDBA-DI shows a small ΔEST and fast kRISC in the doped film and an EQEmax of 32.2% with Commission International de I'Eclairage (CIE; 0.14, 0.15) in the OLED device.
TDBA–DI shows deep-blue emission in toluene and a small singlet–triplet energy gap of 0.11 eV and 20wt%-doped films of TDBA–DI in DBFPO host exhibits high photoluminescence quantum yields of 99%. Fabricated TDBA–DI blue emitting OLED device shows a high external quantum efficiency of 38.15% with low roll-off characteristics of 25.2% at high luminance of up to 5,000 cd m–2. Also TADF devices based on TDBA-DI achieve a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency of 41.2% by using a polymer semiconductor T2fQ as HTL and TSPO1 as ETL materials with suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m–2.