Solving the Interdependence Between Electrical Conductivity and Seebeck Coefficient: A Case Study of PEDOT:PSS.

PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate) is a promising, biocompatible, thermoelectric material with (bi)polaron-type transport properties. Inexpensive, flexible thermoelectric generators based on PEDOT:PSS will have considerable commercial potential for wearable devices such as Internet of Things (IOT), biomedical sensors, even portable electronics. However, thermoelectric performance is still far from that required for practical applications due to the inharmonicity of thermoelectric parameters and a paucity of information on the relationship between molecular structure and Seebeck coefficient. This review introduces the structure-physical property relationships of PEDOT:PSS, and describes recent strategies for decoupling the apparent trade-off between electrical conductivity and Seebeck coefficient. These strategies include thermal treatment of the conductive polymer, secondary doping/dedoping optimization, hybridization, and crystal engineering. While these approaches have been successful in understanding the structure-charge transport relationship in PEDOT:PSS, they have not addressed the influence of secondary and tertiary structure on Seebeck coefficient. The purpose of this review is to provide new insights into the positive Seebeck coefficient dependence on electrical conductivity and to elucidate the independent influences and the synergetic effects of processing and post-treatment strategies.