Highly Ordered Nanoconfinement Effect from Evaporation-Induced Self-Assembly of Block Copolymers on In Situ Polymerized PEDOT:Tos

Abstract

Organic thermoelectric materials based on conducting polymers have focused on increasing electrical conductivity and optimizing thermoelectric properties via dedoping processes. To control the crystallinity and crystal alignment for enhanced electrical conductivity, a confinement geometry in nanostructures with grapho-epitaxial growth of conducting polymers during in situ polymerization could be a promising approach. We obtained highly ordered lamellar, cylindrical and disordered nanostructures from PEO-b-PPO-bPEO block copolymer (BCP) and iron(III) tosylate (Fe(Tos)(3)) oxidant blended films and solvent evaporation induced self-assembly (EISA) processes. Then, in situ vapor phase polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT):Tos on differently ordered oxidant/BCP films was performed. The effect of BCP nanostructures on the crystallinity, crystal orientation and electrical conductivity of the PEDOTs was confirmed by nanostructural and crystallographic analyses using grazing incidence small and wide-angle X-ray scattering (GISAXS and GIWAXS, respectively) experiments before and after polymerization and after a washing process. Different washing solvents also affected the electrical conductance and crystal structure. We achieved thermoelectric thermopowers up to 70 mu W center dot m(-1)center dot K-2 by using an immersion dedoping process to reduce the carrier concentration and enhance the Seebeck coefficient, with little change of crystal structure.