Introducing MR-TADF Emitters into Light-Emitting Electrochemical Cells for Narrowband and Efficient Emission

Organic semiconductors that emit by the process of multi-resonance thermally activated delayed fluorescence (MR-TADF) can deliver narrowband and efficient electroluminescence while being processable from solvents and metal-free. This renders them attractive for use as the emitter in sustainable light-emitting electrochemical cells (LECs), but so far reports of narrowband and efficient MR-TADF emission from LEC devices are absent. Here, this issue is addressed through careful and systematic material selection and device development. Specifically, the authors show that the detrimental aggregation tendency of an archetypal rigid and planar carbazole-based MR-TADF emitter can be inhibited by its dispersion into a compatible carbazole-based blend host and an ionic-liquid electrolyte, and it is further demonstrated that the tuning of this active material results in a desired balanced p- and n-type electrochemical doping, a high solid-state photoluminescence quantum yield of 91%, and singlet and triplet trapping on the MR-TADF guest emitter. The introduction of this designed metal-free active MR-TADF material into a LEC, employing air-stabile electrodes, results in bright blue electroluminescence of 500 cd m(-2), which is delivered at a high external quantum efficiency of 3.8% and shows a narrow emission profile with a full-width-at-half-maximum of 31 nm.

Automated summary

In this study, narrowband and efficient electroluminescence from multi-resonance thermally activated delayed fluorescence (MR-TADF) organic semiconductors in light-emitting electrochemical cells (LECs) is achieved by carefully selecting materials and developing the devices. The aggregation tendency of the MR-TADF emitter is inhibited by dispersing it into a compatible blend host and an ionic-liquid electrolyte. The designed metal-free active MR-TADF material exhibits a high external quantum efficiency of 3.8% with a narrow emission profile.