Improving mobility and electrochemical stability of a water-gated polymer field-effect transistor

• A polymer water-gated field effect transistor based on pBTTT is reported.
• State-of-the-art performances for polymeric electrolyte-gated devices are demonstrated.
• Extracted charge carrier mobility in the order of 0.1 cm2 V−1 s−1.
• Improved electrochemical stability in the voltage operational range.
• First evidenced the key-role of polymer alkyl side chains at the water interface.

Water-gated organic transistors have attracted considerable attention in the field of biosensors, thanks to their capability of operating in the aqueous environment typical of biological systems at very low voltages (∼1 V). Some examples have been recently reported in the literature, employing different organic materials as the active semiconducting layer, ranging from small molecules to single crystals. Here we report on water-gated polymer-based organic-field effect devices using poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT) as the active layer. Very promising electronic performances, in terms of mobility and operating voltages are obtained; notably, the charge carrier mobility is in the order of 0.08 cm2/V s, which is of the same order of magnitude of values reported for single-crystal based water-gated devices, and consistent with values reported for solid-state polymer dielectric transistors. Moreover, the pBTTT-based device shows improved electrochemical stability, as compared to previously reported polymer based water-gated devices. Importantly, good functioning of the device is demonstrated also when water is replaced by physiological-like solutions. Critical to the transistors operation, besides the good transport properties of the active material, is the key-role played by alkyl side chains and ordered morphology of the polymer at the interface with the liquid environment, which we highlight here for the first time. Our contribution overall provides a useful step towards the development of bio-organic sensors, with enhanced properties in terms of sensitivity and stability, and for a successful exploitation of organic based field effect transistors in biotic/abiotic interfaces.

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