Rigid indolocarbazole donor moiety for highly efficient thermally activated delayed fluorescent device

Abstract A new rigid donor moiety, namely, triphenyl-substituted indolocarbazole for thermally activated delayed fluorescence (TADF) materials is reported. Based on this donor, two novel TADF emitters 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho [3,2,1-de]anthracen-7-yl)-6,11,12-triphenyl-5,11-dihydroindolo [3,2-b]carbazole (TDBA-TPDICz) and 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-6,11,12-triphenyl-5,11-dihydroindolo [3,2-b]carbazole (TRZ-TPDICz) are synthesized and evaluated as TADF emitters. The phenyl substitutions at 6, 12-positions of donor moiety increase the steric hindrance between the donor and the acceptor resulting in increase in dihedral angle between them. As a consequence, the change in the TADF properties of these emitters are analyzed by photophysical, electrochemical properties and compared with the analogs reference material 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-11-phenyl-5,11-dihydroindolo [3,2-b]carbazole (TRZ-pIC). Further, the TADF device fabricated with TDBA-TPDICz shows the deep blue color CIE coordinates of (0.14, 0.14) with a maximum external quantum efficiency (EQE) of 16.9% and maximum current efficiency (CE) of 21.4 cd/A. Meanwhile, the device using TRZ-TPDICz emitter achieve a maximum EQE of 30.3% and a maximum CE of 77.4 cd/A at green color CIE coordinates of (0.25, 0.53). This result is superior than the TRZ-pIC reference material.