Fabrication and characterisation of a flexible thermoelectric generator using PANI/graphite/bismuth telluride composites

Unique thermoelectric properties of low-cost, widely available conducting polymers and multi-layered graphite structures have motivated the development of flexible thermoelectric generators using screen printing for low-temperature applications. Composites of polyaniline and graphite in different ratios with one weight percentage of bismuth telluride were prepared to fabricate flexible thermoelectric generators. The performance of the devices showed that the addition of graphite to polyaniline reduced the band gap energy from 2.90 to 1.33 eV, which was further reduced to 1.05 eV upon the addition of bismuth telluride. Adding graphite and bismuth telluride to polyaniline increased carrier mobility from 0.12 to 0.41 cm² V⁻¹ s⁻¹ without affecting carrier concentrations. An optimum concentration of graphite reduced transient thermal conductivity. A flexible thermoelectric generator with a polyaniline to graphite ratio of 1 : 2 and 1 weight percentage of bismuth telluride exhibited superior performance with the maximum Seebeck coefficient, power factor and power output of 39.14 μV K⁻¹, 0.29 nW m⁻² K⁻² and 0.58 nW, respectively, at a temperature difference of 90 °C, which are 4.0, 5.8 and 6.1 times higher than those of the pure polyaniline-based device. Further increase in the polyaniline to graphite ratio of the composite increased both transient thermal conductivity and resistivity, resulting in the reduction of the Seebeck coefficient and power factor.