Hybridized local and charge transfer dendrimers with near-unity exciton utilization for enabling high-efficiency solution-processed hyperfluorescent OLEDs

Abstract

Achieving both high emission efficiency and exciton utilization efficiency (η_S) in hot exciton materials is still a formidable task. Herein, a proof-of-concept design for improving η_S in hot exciton materials is proposed via elaborate regulation of singlet–triplet energy difference, leading to an additional thermally activated delayed fluorescence (TADF) process. Two novel dendrimers, named D-TTT-H and D-TTT-^tBu, were prepared and characterized, in which diphenylamine derivatives were used as a donor moiety and tri(triazolo)triazine (TTT) as an acceptor fragment. Compounds D-TTT-H and D-TTT-^tBu showed an intense green color with an emission efficiency of approximately 80% in solution. Impressively, both dendrimers simultaneously exhibited a hot exciton process and TADF characteristic in the solid state, as was demonstrated via theoretical calculation, transient photoluminescence, magneto-electroluminescence and transient electroluminescence measurements, thus achieving almost unity η_S. A solution processable organic light-emitting diode (OLED) employing the dendrimer as a dopant represents the best performance with the highest luminance of 15090 cd m⁻² and a maximum external quantum efficiency (EQE_max) of 11.96%. Moreover, using D-TTT-H as a sensitizer, an EQE_max of 30.88%, 24.08% and 14.33% were achieved for green, orange and red solution-processed OLEDs, respectively. This research paves a new avenue to construct a fluorescent molecule with high η_S for efficient and stable OLEDs.