Electrolyte-gated organic transistors offer low bias operation facilitated by direct contact of the transistor channel with an electrolyte. Their operation mode is generally defined by the dimensionality of charge transport, where a field-effect transistor allows for electrostatic charge accumulation at the electrolyte/semiconductor interface, whereas an organic electrochemical transistor (OECT) facilitates penetration of ions into the bulk of the channel, considered a slow process, leading to volumetric doping and electronic transport. Conducting polymer OECTs allow for fast switching and high currents through incorporation of excess, hygroscopic ionic phases, but operate in depletion mode. Here, we show that the use of glycolated side chains on a thiophene backbone can result in accumulation mode OECTs with high currents, transconductance, and sharp subthreshold switching, while maintaining fast switching speeds. Compared with alkylated analogs of the same backbone, the triethylene glycol side chains shift the mode of operation of aqueous electrolyte-gated transistors from interfacial to bulk doping/transport and show complete and reversible electrochromism and high volumetric capacitance at low operating biases. We propose that the glycol side chains facilitate hydration and ion penetration, without compromising electronic mobility, and suggest that this synthetic approach can be used to guide the design of organic mixed conductors.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We thank I. Uguz (CMP-EMSE) for fruitful discussion and help in fabrication. This work was carried out with financial support from European Commission (EC) FP7 Project SC2 (610115), EC FP7 Project ArtESun (604397), EC FP7 Project PolyMed (612538), and Engineering and Physical Sciences Research Council (EPSRC) Project EP/G037515/1. E.B. thanks the Spanish Ministry of Economy and Competitiveness for his predoctoral contract. M.S. acknowledges support from the first edition of the BBVA Foundation Grants for Researchers and Cultural Creators.