Nanostructured PEDOT-based multilayer thin films with high thermoelectric performances

Intrinsically conductive polymers are considered as one of the most promising candidates for thermoelectric (TE) materials due to their outstanding properties. Prior studies have been primarily focused on conducting polymers such as polyaniline, polypyrrole, polythiophene, and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). In particular, currently available cationic water-soluble conjugated polymers are limited because of difficulties in synthetic routes. Herein, a positively charged PEDOT nanoparticles (PEDOT:NPs) dispersed in water are synthesized to serve as a structure directing agent for the development of hierarchical architectures with high flexibility and TE performances. A completely organic composite is fabricated by alternately depositing layers of aqueous solutions of PEDOT:NPs and double-walled carbon nanotubes (DWNT) stabilized with PEDOT:PSS via a layer-by-layer methodology. A 20 bilayer thin film (≈ 2.1 µm thick), comprised of a PEDOT:NPs/DWNT-PEDOT:PSS repeating sequence, exhibits high electrical conductivities of up to 744 S cm⁻¹ and a high Seebeck coefficient up to 83 µV K⁻¹. As a result, the multilayer thin films achieve a power factor of 512 µW m⁻¹ K⁻². These excellent TE properties can be attributed to the formation of a three-dimensional conjugated network with a highly ordered structure, which facilitates carrier transport within the film. This organic composite, based on a newly synthesized conducting polymer, with high flexibility and power factor offers a promising route to utilize efficient thermoelectric devices on flexible surfaces.