Sequential doping of solid chunks of a conjugated polymer for body-heat-powered thermoelectric modules

Abstract

Sequential doping of 1 mm3 sized cubes of regio-regular poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-tetracyanoquinodimethane is found to result in a doping gradient. The dopant ingresses into the solid material and after two weeks of sequential doping yields a 250 μm thick doped surface layer, while the interior of the cubes remains undoped. The doping gradient is mapped with energy dispersive x-ray spectroscopy (EDX), which is used to estimate a diffusion coefficient of 1 × 10−10 cm2 s−1 at room temperature. The cubes, prepared by pressing at 150 °C, feature alignment of polymer chains along the flow direction, which yields an electrical conductivity of 2.2 S cm−1 in the same direction. A 4-leg thermoelectric module was fabricated with slabs of pressed and doped P3HT, which generated a power of 0.22 μW for a temperature gradient of 10.2 °C generated by body heat.