Giant Seebeck Effect in PEDOT Materials with Molecular Strain

Poly 3,4-ethylenedioxythiophene (PEDOT) has been attracting attention as a thermoelectric material for room-temperature use due to its flexibility and non-toxicity. However, PEDOT reportedly generates insufficient thermoelectric power for practical use. This work tried to improve the Seebeck coefficient by introducing molecular strain to PEDOT molecules by loading a Polystyrene sulfonate (PSS)-free PEDOT on a Polyethyleneterephthalate (PET) fiber. Raman spectroscopy revealed the PEDOT materials with significant compression in the C{\alpha}-C{\alpha} bond and extension in the C{\alpha}=C\b{eta} bond exhibit Seebeck coefficients two orders of magnitude larger than usual. Furthermore, strain in the C\b{eta}-C\b{eta} bond strongly correlated with the Seebeck coefficient that varied in a broad range from -2100 to 3100 {\mu}V K-1. This variation indicated that the molecular strain formed a sharp peak or valley around the Fermi level in the density of state (DOS) function, which gradually shifts along with the C\b{eta}-C\b{eta} strain. This molecular strain-induced giant Seebeck effect is expected to be an applicable technique for other polythiophene molecules.