Multi-resonant thermally-activated delayed fluorescence (MR-TADF) emitters for blue organic light-emitting transistors (OLETs)

Thermally-activated delayed fluorescence (TADF) molecules are a promising class of emitters for organic optoelectronic devices, potentially more efficient than phosphorescent emitters. Among them, multi-resonant TADF (MR-TADF) emitters are designed to enhance the rigid molecular structure, leading to a narrow-band emission below 50 nm. In this work, we studied a multi-resonant TADF material, t-DABNA, embedded in DPEPO as a blue emissive layer in organic light-emitting transistors (OLETs), a device platform that combines into a single device the switching capability of a transistor and the light emission of an organic light-emitting diode. We investigated the effect of different t-DABNA concentrations within the emissive blend in a multilayer heterostructure, and we analyzed our experimental results in terms of optical, morphological, and optoelectronic properties of the blend itself. We found that emitter content of approximately 10% leads to the highest external quantum efficiency (0.18%) in the devices and with a narrow band emission as low as 30 nm. This work offers key insights into the use of MR-TADF emitter molecules within organic field-effect light-emitting devices.