TADF-FIELD: TADF emitters field-effect light-emitting devices

(Academy of Finland, 2023-2027)

Thermally-activated delayed fluorescence allows for excitons from the triplet state to be harnessed from the singlet state by reverse intersystem crossing through thermal activation. Since the first report on TADF by Adachi in 2012, TADF molecules have been successfully exploited to achieve heavy-metal-free phosphorescent emitter-based devices (mainly OLEDs) with high brightness, state-ofthe-art color coordinates and efficiency exceeding 30%.

In this scenario, TADF-FIELD will address the following research question:

Can field-effect transport improve the emission in TADF-based light-emitting transistor?

We aim at identifying the effect of an external horizontal field on the delayed fluorescence mechanism, with a particular focus on exciton formation and dynamics, while at the same time extend the use of TADF materials to the organic light-emitting transistor (OLETs) platform for improved performances. As first step, out approach is mainly experimental and includes both the study of materials (optical/electronic properties of TADF molecules) and their implementation in device architectures.

We propose to use a multi-layer heterostructure fabricated in vacuum to control morphology of different layers and corresponding interfaces. By combining optoelectronic device characterization with the study of the optical response in our materials, we expect to gain a deeper insight into TADF mechanism and its photophysics as well as some of the key processes in the device, including field-effect transport and light emission.

The experimental activity is organized in three main work packages, each including several tasks, which, once individually and independently completed, will naturally lead to the successful completion of the project. Our methodology is designed as a step-by-step incremental process, where each task can be accomplished on previous gained knowledge. We expect our results to be of interest in the short-term mainly for the scientific community; then, with the consolidation of TADF-based transistors, this will surely gather the attention of R&D companies working in this sector. These will enable significantly improved and cheaper devices, of relevance for example for displays and lighting applications. In the long-term (>10yrs), this will reduce the need for expensive and rare metals, leading to a significant economical, global, and societal impact.