High-efficiency blue organic light-emitting Diodes using emissive carbazole-triazine-based donor-acceptor molecules with high reverse intersystem crossing rates

Abstract

We report blue thermally activated delayed fluorescent (TADF)organic light emitting diodes(OLEDs) with high efficiencies which areattributed toemployingdonor-acceptor type TADF compounds having highreverse intersystem crossing (RISC)rates. Carbazole derivatives and a triphenyltriazine (or a dibenzothiophene) are employed as the donor (D) and the acceptor (A)moieties, respectively. We can achieve four D-A type blue TADF compounds through the combination of the moieties and adjust the energy gap between the lowest excited singlet and triplet statesand accordingly the RISC rate (k(RISC)) for the compounds. A blue OLED using one of the TADF molecules,9-(9H-carbazol-9-yl)-12-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)pheny1)-5-phenyl-5,12-dihydroindolo[3,2-a]carbazole exhibitshigh maximum external quantum efficiency (22.3%)due to itsshort excitonlifetime (6.1 mu s) induced by its highk(RISC) (1.825 x 10(6) s(-1)).