Conducting polymers, known for many years for their interesting electrical, optoelectronic, and mechanical properties, and good processability even on flexible substrates, are nowadays studied for their thermoelectrical properties. Among them, poly(3,4-ethylenedioxythiophene) (PEDOT) is certainly the most investigated and the most used conductive polymer and recent studies have led to high conductivity enhancements.[1] However, an exhaustive understanding of the mechanisms governing such enhancement is still lacking, hindered by the semi-crystalline nature of the material itself. In this lecture, we will present 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) trifluoro-methanesulfonate as oxidant, N-methyl-pyrrolidone as polymerization rate controller and organic or sulfuric acid as dopant.[2] 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. We propose a charge transport model that fully corroborates our experimental observations. Our PEDOT-based materials exhibit conductivities up to 5400 S cm-1 and transmittance at 550 nm between 80 and 96 %. In the last part of this lecture we will discuss their thermoelectric properties and we will show their high potential for application in thermoelectric devices and all-polymeric flexible transparent heaters.[3] References: [1] M. N Gueye, A. Carella, J. Faure-Vincent, R. Demadrille, J-P. Simonato, "Progress in understanding structure and transport properties of PEDOT-based materials: a critical review", Prog. Mater. Sci., 2018, Submitted. [2] M. N. Gueye, A. Carella, N. Massonnet, E. Yvenou, S. Brenet, J. Faure-Vincent, S. Pouget, F. Rieutord, H. Okuno, A. Benayad, R. Demadrille, J-P. Simonato, “Structure and Dopant Engineering in PEDOT Thin Films: Practical Tools for a Dramatic Conductivity Enhancement”, Chem. Mater., 2016, 28, 3462-3468. [3] M. N Gueye, A. Carella, R. Demadrille, J-P. Simonato, “All-Polymeric Flexible Transparent Heater”, ACS Appl. Mater. Interfaces, 2017, 9, 27250-27256 Acknowledgements: The authors acknowledge the LABEX Laboratoire d’Alliances Nanosciences-Energies du Futur (LANEF, ANR-10-LABX-51-01) for funding the MNG Ph.D and CEA for funding the OB and AS Ph.D. The authors acknowlege ANR for partial funding throw "Harvesters" project (ANR-16-CE05-0029).