Reverse intersystem crossing accelerating assistant dopant for high efficiency and long lifetime in red hyperfluorescence organic light-emitting diodes

A highly efficient deep-red hyperfluorescence device achieving long device lifetime was fabricated by adopting a newly designed 2,5-bis(12H-benzo[4,5]thieno[2,3-a]carbazole-12-yl)-3,6-di(9H-carbazol-9-yl)terephthalonitrile (12BTCzTPN) thermally activated delayed fluorescence (TADF) assistant dopant. The 12BTCzTPN was designed via donor modification of 2,3,5,6-tetra(9H-carbazol-9-yl)terephthalonitrile (4CzTPN) to increase reverse intersystem crossing (RISC) rate for fast up-conversion. The carbazole donor moiety was replaced with 12H-benzo[4,5]thieno[2,3-a]carbazole (12BTCz) donor, which induced a small singlet–triplet energy gap and large spin–orbit coupling via the heavy atom effect of sulfur, resulting in 4.5-times faster RISC rate than the 4CzTPN TADF molecule. The addition of 12BTCzTPN as an assistant dopant to a deep-red hyperfluorescence device resulted in a device with a high external quantum efficiency of 19.9% and a long device lifetime of 1312 h at 3000 cd/m², which is up to 90% of the initial luminance.