Thermoelectric polymer composite yarns and an energy harvesting wearable textile

A thermoelectric wearable is proposed based on an innovative 3D wearable design, with p- type polymer impregnated cotton yarns and n-type polymer impregnated cotton yarns, where the ratio of the p-/n-type yarn cross-sections is optimised to maximise the thermoelectric conversion efficiency. The thermoelectric yarns are embroidered through a double-layer cotton fabric, using plain-stitch, and connected via painted silver electrodag patches. The first stage of this study involved the characterisation of P3HT-, PEDOT:PSS- and PCBM-cotton fabric composite samples, in terms of their fibre volume fraction, specific heat capacity, thermal conductivity, electrical conductivity, Seebeck coefficient, Z and power factors. In this initial assessment, P3HT was selected as the p-type polymer compared to PEDOT:PSS, and PCBM was selected as the n-type polymer. A small, 3D wearable prototype was fabricated and tested: it exhibited a Seebeck coefficient of 380 μV K⁻¹ but a relatively high resistance. It was estimated that scaling up this thermoelectric wearable to body coverage would produce about 1.5–2 μW for a temperature difference of 40 °C applied on the thermoelectric device. (paper)