Suppression of Dexter Energy Transfer through Modulating Donor Segments of Thermally Activated Delayed Fluorescence Assistant Dopants.

Device degradation in red hyperfluorescent organic light-emitting diodes is primarily caused by exciton energy loss due to Dexter energy transfer (DET) from a thermally activated delayed fluorescence (TADF) assistant dopant to a fluorescent dopant. In this work, the donor segments in the TADF assistant dopants were delicately modulated to suppress DET for high efficiency. The derived benzothienocarbazole donors were introduced to the TADF assistant dopants instead of carbazole, and they accelerated the reverse intersystem crossing of the TADF assistant dopant and managed the DET from the TADF assistant dopant to the fluorescent dopant. As a result, the red TADF-assisted device showed a high external quantum efficiency of 14.7% and improved the device lifetime by 70% compared to a well-known TADF-assisted device.