SCIENTIFIC HIGHLIGHTS RL4, Articles

Ambipolar solution processed organic field-effect transistors (OFETs) and water-gated OFET with carbon-composite gate contact

Unconventional solution processed organic field-effect transistors (OFETs): charge transfer complex as ambipolar semiconductor and carbon composite gate in electrolyte-gated OFET

Solution processed organic field-effect transistors (OFETs) are raising great interest for the development of low-cost electronics. Despite the impressive progress achieved in the last years, there is still plenty of room in terms of material engineering. Here, we highlight two recent works where we have used an unconventional material as active ambipolar semiconductor and another one where an alternative carbon-based electrode has been exploited as gate contact.

1) Charge transfer (CT) complexes are composed of a donor and acceptor molecule that crystallize together either in segregated or alternated stacks. They have been studied for a long time as organic conductors and, recently have also been attracting great interest as potential candidates for ambipolar semiconductors. However, their application in OFETs has been limited to ideal single crystals or to evaporated films, hindering their potential for real applications. Here, we report the preparation of thin films of a CT complex using a simple solution shearing technique and blending the precursors with a binding polymer. The resulting OFET devices exhibited ambipolar field-effect in environmental conditions. Thus, this work opens new perspectives for the application of CT complexes in electronic devices.

2) Nanocomposite paste electrodes using carbon nanotubes (CNTs) have been investigated for the first time in electrolyte-gated organic field-effect transistors (EGOFETs) as a replacement of conventional metal gate electrodes. The potential of using such non-conventional gate electrodes for sensing purposes has also been evaluated by investigating, as a proof of concept, the formation of a supramolecular complex between a CNT functionalised with β-cyclodextrin (β-CD) as a bio-recognition element and tryptophan, giving detection limits at picomolar levels. Accordingly, carbon-composite electrodes have been demonstrated to be a potential alternative to metal gate electrodes for the development of a new generation of highly sensitive carbon-based EGOFET bio-sensors.

Carbon-paste nanocomposites as unconventional gate electrodes for electrolyte-gated organic field-effect transistors: electrical modulation and bio-sensing
Jose Muñoz, Francesca Leonardi, Tayfun Özmen, Marta Riba-Moliner, Arantzazu González-Campo, Mireia Baeza, Marta Mas-Torrent
J. Mater. Chem. C 2019, 7, 14993
DOI: 10.1039/C9TC04929K

Solution-processed thin films of a charge transfer complex for ambipolar field-effect transistors
Tommaso Salzillo, Antonio Campos, Marta Mas-Torrent
J. Mater. Chem. C 2019, 7, 1025
DOI: 10.1039/C9TC03064F

Figure: (Left) Crystalline thin film of a charge transfer complex prepared from a solution of a donor and acceptor molecules blended with polystyrene as a binding polymer. (Right) Electrolyte-gated field-effect transistor in which the gate contact is a composite carbon based electrode composed of carbon-nanotubes functionalised with β-cyclodextrines.

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