Poly(3,4-ethylenedioxythiophene) (PEDOT) is certainly the most known and most used conductive polymer since it is commercially available and shows great potential for organic electronic, photovoltaic and thermoelectric applications. Studies dedicated to PEDOT films have led to high conductivity enhancements. However, an exhaustive understanding of the mechanisms governing such enhancement is still lacking, hindered by the semi-crystalline nature of the material itself. We report the development of highly conductive PEDOT films by controlling the crystallization of the PEDOT chains and by a subsequent dopant engineering approach using iron (III) trifluoromethanesulfonate as oxidant, N-methyl pyrrolidone as polymerization rate controller and sulfuric acid as dopant. XRD, HRTEM, Synchrotron GIWAXS analyses and conductivity measurements down to 3 K allowed us to unravel the organization, doping and transport mechanism of these highly conductive PEDOT materials. N-methyl pyrrolidone promotes bigger crystallites and structure enhancement during polymerization while sulfuric acid treatment allows the replacement of triflate anions by hydrogenosulfate and increases the charge carrier concentration. We finally propose a charge transport model that fully corroborates our experimental observations. These polymers exhibit conductivities up to 5400 S cm<sup>-1</sup>, Seebeck coefficient at 18 µV K<sup>-1</sup> and transmittance at 550 nm between 80 and 96 % and thus show great promise for the replacement of ITO as transparent electrode in transparent film heater applications or as thermoelectric material for room temperature energy harvesting.

Structure and dopant engineering in PEDOT thin films for the development of all-polymeric transparent heaters and thermoelectric applications

2019 Fall National Meeting

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