Strategically Tailoring Porous Polythiophene Nanofibers in Organic Electrochemical Transistors To Facilitate the Anion Doping

The nanofiber microstructure is porous and can maintain the crystallinity of conjugated polymers during ion doping and dedoping. However, there is no report about applying self-assembled conjugated polymers with a nanofiber microstructure in organic electrochemical transistors (OECTs). Therefore, this study aimed to enhance the OECT performance by fabricating thin films using a self-assembly method with poly(3-hexylthiophene) (P3HT) as the active layer. The nanofiber microstructure can also provide a porous interface to electrolytes and facilitate ion penetration and doping of the conjugated polymers. The P3HT nanofibers are fabricated through self-assembly in a mixed solvent system and further refined with ultrasonication and UV irradiation. In situ electrochemical–optical analysis, ex situ grazing-incidence wide-angle X-ray scattering, and atomic force microscopy are utilized for structural analysis to gain deeper insight into the morphology of the thin films and their impact on device performance. An aqueous KPF6 electrolyte is selected and applied in the OECT device characterizations. This addressed the instability issues associated with hydrophilic electrolytes like KCl. Among the different configurations tested, the nanofibers undergoing ultrasonication and without UV irradiation demonstrate excellent electrical properties and stabile performance with high hole mobility (μh) of 0.385 cm2 s–1 V–1 and OECT figure-of-merits (μC*) of 60.58 F s–1 cm–1 V–1, which is significantly better than the film counterpart with μh of 0.190 cm2 s–1 V–1 and μC* of 20.83 F s–1 cm–1 V–1, suggesting that the well-ordered nanofibrillar structure effectively facilitates charge transport in the OECT. The results of this study provide a new design approach to tailoring fibrillar and porous microstructures in conjugated polymers to promote their ion-doping capability and charge transport in OECT applications.