The rapid growth of wearables has created a demand for lightweight, elastic and conformal energy harvesting and storage devices. The conducting polymer poly(3,4-ethylenedioxythiophene) has shown great promise for thermoelectric generators, however, the thick layers of pristine poly(3,4-ethylenedioxythiophene) required for effective energy harvesting are too hard and brittle for seamless integration into wearables. Poly(3,4-ethylenedioxythiophene)-elastomer composites have been developed to improve its mechanical properties, although so far without simultaneously achieving softness, high electrical conductivity, and stretchability. Here we report an aqueously processed poly(3,4-ethylenedioxythiophene)-polyurethane-ionic liquid composite, which combines high conductivity (>140 S cm⁻¹) with superior stretchability (>600%), elasticity, and low Young’s modulus (<7 MPa). The outstanding performance of this organic nanocomposite is the result of favorable percolation networks on the nano- and micro-scale and the plasticizing effect of the ionic liquid. The elastic thermoelectric material is implemented in the first reported intrinsically stretchable organic thermoelectric module.

Conducting polymers have recently been suggested as thermoelectric materials for use in large-area thermogenerators. To help assessing the feasibility of this the electrical conductivity and Seebeck coefficient of a series of heavily doped regioregular poly(3-hexylthiophene) films are measured between 220 and 370 K. p-type chemical doping of up to 34% is accompanied by the introduction of negatively charged counterions, PF6$-${}. The counterions produce a disordered environment within which the p-type electronic carriers move. This disorder diminishes with increasing doping as the effect of the counterions is smoothed out. Concomitantly the thermally activated electrical conductivity rises strongly while its activation energy decreases. On the other hand, the Seebeck coefficient is found to be weakly dependent on temperature and it decreases with increasing doping. When combined, these results indicate that the thermoelectric power factor reaches a broad maximum between 20% and 31% doping. These results are discussed in terms of the thermally activated hopping-type mobility of bipolarons, deduced from the absence of electron spin resonance signal in the heavily doped materials.