Highly Conductive n-Type Polymer Fibers from the Wet-Spinning of n-Doped PBDF and Their Application in Thermoelectric Textiles

Abstract

The field of electronic textiles currently lacks n-type polymer fibers that can complement the more established p-type polymer fibers. Here, a highly conductive n-type polymer fiber is obtained via wet-spinning of n-doped poly(3,7-dihydrobenzo[1,2-b:4,5-b’]difuran-2,6-dione) (n-PBDF). The electrical conductivity of the fibers increases from 1000 to 1600 S cm−1 with increased draw during processing and correlates well with Young's modulus. Wide-angle X-ray scattering reveals the existence of a bimodal orientation of the polymer chains, favoring parallel alignment to the fiber axis with increased draw. After 14 d in 80% humid air, fiber conductivity stabilizes maintaining 81% of the initial conductivity. Although the electrical conductivity drops slightly over time, the Seebeck coefficient increases, resulting in the highest thermoelectric power factor being measured at 91 µW m−1 K−2 for the most drawn fiber 14 d after its fabrication. A proof-of-concept two-couple thermoelectric textile is crafted by embroidering bundles of n-type PBDF fibers and p-type PEDOT:PSS fibers. The device generates 2.40 nW at a 22 °C temperature gradient. This work represents the initial steps and a crucial advancement toward fabricating high-performance n-type polymer fibers that can complement their p-type counterparts to close the existing performance gap.