Aryl-Annulated [3,2- a ] Carbazole-Based Deep-Blue Soluble Emitters for High-Efficiency Solution-Processed Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes with CIE y <0.1.

In this study, we demonstrated two deep-blue TADF emitters, BO-tCzPhICz and BO-tCzDICz, for solution-processable thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). They were synthesized by employing an organoboron acceptor and 9-(3,6-di- tert -butyl-9 H -carbazol-9-yl)-5-phenyl-5,12-dihydroindolo[3,2- a ]carbazole (tCzPhICz) and 12-(3,6-di- tert -butyl-9 H -carbazol-9-yl)-15 H -diindolo[2,3- b :1',2',3'- lm ]carbazole (tCzDICz) as bulky aryl-annulated [3,2- a ] carbazole donors, respectively. Both emitters showed sufficient solubility in organic solvents, narrow deep-blue emission, and small energy difference (Δ E ST ) between singlet and triplet states, which can be applied to solution-processable deep-blue TADF-OLEDs. Solution-processed OLEDs exploiting these TADF emitters displayed deep-blue electroluminescence with CIE y <0.1, and high external quantum efficiencies of 17.8 and 14.8% were observed for BO-tCzPhICz and BO-tCzDICz, respectively. The emitter bearing bulky ICz-based donating units shows highly promising potential for high-efficiency solution-processable deep-blue TADF-OLEDs.