Anionic conduction mediated giant n-type Seebeck coefficient in doped Poly(3-hexylthiophene) free-standing films

The present work demonstrates a totally radical change in conduction nature from typical p-type to n-type through ionic transport in FeCl3 doped free-standing poly(3-hexylthiophene) (P3HT) films. The thermodiffusion of Cl− ions generated a giant negative Seebeck coefficient (∼2.7 mV/K) and a moderately high electrical conductivity (∼1 S/cm); an unprecedented level in polymers. A thermoelectric power generator fabricated using these P3HT films delivered an output electrical power of 25 μW with open circuit voltage of 128 mV for a ΔT of 46 °C. Though continuous operation reduced the output power due to inability of the ions to pass through the interface between doped P3HT and metallic contact, yet the generated voltage was found to be quite stable over a period of 1 h under load. With such a high n-type Seebeck coefficient, free-standing P3HT films show a great potential for energy harvesting from intermittent heat sources as well as in supercapacitor charging for futuristic energy storage devices. Thermo-diffusion of Cl− ions through Soret effect in FeCl3 doped poly(3-hexylthiophene) films resulted in n-type conduction and generated a giant negative Seebeck coefficient (∼2.7 mV/K). [Display omitted] •Soret effect in FeCl3 doped poly(3-hexylthiophene) films caused n-type conduction.•Thermodiffusion of Cl− ions generated giant negative Seebeck coefficient (∼15mV/K).•A relatively high electrical conductivity (∼1 S/cm) could simultaneously be achieved.•P3HT films’ device delivered output electrical power of 25.5 μW for ΔT ∼46°C.