Printed, cost-effective and stable poly(3-hexylthiophene) electrolyte-gated field-effect transistors

Organic bioelectronic sensors based on an electrolyte gated field-effect transistor are gaining momentum due to their extraordinary high-performance level that enables label-free selective single-molecule detection of both genomic and protein biomarkers with a millimeter-wide electrolyte-gated field-effect transistor (EGOFET) device. The organic semiconductor channel material used so far is a spin-coated regio-regular poly(3-hexylthiophene) (P3HT). Of paramount importance is to design an EGOFET sensor that is stable and cost-effective. To address the latter feature, an ink-jet printed regio-regular P3HT film is here investigated as the channel material. Moreover, the EGOFET device structure is intended to comprise a coplanar lateral gate electrode that enables mechanical and electrical stability. Overall, the structure is compatible with large area processing so it can be fabricated at low-costs and can be operated continuously for eight days. Additionally, systematic optical and Raman characterization of the P3HT film proves that the printing process results in a film with a low energetic disorder (better π-π stacking in the crystalline regions) that likely enables stable operation. However, the higher quality crystalline regions (as compared to a spin-coated film) are dispersed in a more significant fraction of the amorphous disordered material with a larger amount of trap states. The higher crystalline order is ascribed to the higher boiling point and slower evaporation of the ortho-dichlorobenzene solvent used in the printing process. Overall, the present study provides a systematic insight into the structure-property correlations, essential to design a well-functioning and cost-effective EGOFET for high-performance electronic biosensing. It also provides one of the few investigations comparing the features characterizing a spin-coated and an ink-jet printed P3HT film.