For the emerging fields of biomedical diagnostics and environmental monitoring, where sensor platforms for in-situ sensing of ions and biological substances in appropriate aqueous media are required, electrolyte-gated organic fieldeffect transistors (EGOFETs) seem to be the transducers of choice. Due to the formation of an electric double layer at the electrolyte/organic semiconductor interface, they exhibit a very high capacitance allowing for low-voltage and waterstable operation. In combination with the outstanding properties of organic devices like biocompatibility, lowtemperature processability on flexible substrates, as well as the possibility to tune the physical and chemical properties enhancing the selectivity and sensitivity, EGOFET-based sensors are a highly promising novel sensor technology. In order to obtain a reliable sensor response, a stable device operation is crucial. Within this context, we present a combined study of poly(3-hexylthiophene)–based EGOFETs on various substrates. In particular, the influences of different concentrations of NaCl in the electrolyte and various gate electrode materials, to tune the threshold voltage have been investigated. Furthermore, the limits of the stable operational window are evaluated and the effects when abandoning the latter are discussed.
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