Ambipolar high-mobility polymer transistors enabled by Gaussian tail states in nanofiber structures through hopping transport

Flexible polymer transistors are key components in emerging sensor technologies, such as electronic skin for next-generation biomedical prosthetics, and their charge transport mechanisms differ fundamentally from those of conventional inorganic semiconductors. In this work we report the fabrication of an ambipolar polymer field-effect transistor capable of transporting both electrons and holes. The devices are synthesized using a nanoelectrochemical cyclic voltammetry method, which enables the formation of HCl-doped polyaniline nanofibers. These nanofibers introduce Gaussian-distributed tail states within the energy gap, thereby facilitating ambipolar transport. Electrical characterization is carried out through ${I}_{\mathrm{D}}\text{\ensuremath{-}}{V}_{\mathrm{D}}$ and ${I}_{\mathrm{D}}\text{\ensuremath{-}}{V}_{\mathrm{G}}$ measurements as well as temperature-dependent resistivity and mobility studies from 300 K down to 24 K. Analysis of the temperature-dependent mobilities using the multiple trapping and release and the variable-range hopping (VRH) models reveals that electron transport is predominantly governed by VRH, while hole transport shows weaker agreement with either model. Three device types with different carrier densities provide a useful platform for controlling carrier populations and for investigating dual-carrier transport across distinct temperature regimes. The results demonstrate that the nanofiber morphology, combined with hopping transport, enhances electron-electron interactions and broadens the energy gap through Gaussian tail states. This broadened tail-state band enables efficient ambipolar transport, yielding a high field-effect mobility of approximately $4\phantom{\rule{0.28em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, representing a significant advancement in conducting polymer transistors.