Abstract
Despite the great potential of polymer microfibers in human-friendly wearable electronics, most previous polymeric electronics have been limited to thin-film-based devices due to practical difficulties in fabricating microfibrillar devices, as well as defining the active channel dimensions in a reproducible manner. Herein, we report on conducting polymer microfiber-based organic electrochemical transistors (OECTs) and their application in single-strand fiber-type wearable ion concentration sensors. We developed a simple wet-spinning process to form very conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) microfibers using aqueous sulfuric acid solutions and carefully examined their electrical/electrochemical properties. In conjunction with fabricating substrate-free PEDOT:PSS microfiber-based OECT devices, the proposed novel characterization method demonstrated that the current variation ratio can be a reliable method for evaluating the device performance for sensing ion concentrations, regardless of the actual channel dimensions. Finally, we developed single-strand fiber-type skin-mountable OECTs by introducing a source-gate hybrid electrode and demonstrated that the resultant microfiber sensors can perform real-time repetitive measurements of the ion concentration in human sweat.
Highlights
Over the last several decades, field-effect transistors (FETs) have been widely used in various electronic devices, including integrated circuits, display panels, radiofrequency identification readers, and wearable/ implantable biomedical devices, benefiting from the efficient current/voltage amplification modulated by the gate bias
In organic electrochemical transistors (OECTs), conducting polymers are typically utilized as the active channel layer, where the source-todrain current is efficiently modulated by an in-situ doping/dedoping process in the presence of small mobile ions
Due to the rapid coagulation of PEDOT:PSS in the presence of sulfuric acid, the flow of the PEDOT:PSS solution injected through a syringe needle could be transformed into a continuous fiber-shaped PEDOT:PSS solid (Fig. 1b) having a circular/oval cross-section with a rough surface topography, as shown in the SEM images; the overall cross-sectional area of the solid could be controlled by changing the diameter of the needle and/or the acid concentration in the coagulation bath
Summary
Over the last several decades, field-effect transistors (FETs) have been widely used in various electronic devices, including integrated circuits, display panels, radiofrequency identification readers, and wearable/ implantable biomedical devices, benefiting from the efficient current/voltage amplification modulated by the gate bias. The microfiber-based substrate-free three-terminal OECT devices were fabricated via metal wiring, with the effect of the coagulation medium acidity on the corresponding OECT characteristics cautiously examined in terms of the device response to various concentrations of aqueous ionic solutions in contact with the channel layer and the Ag/AgCl gate electrode.
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