Deciphering the quaternary structure of PEDOT:PSS aqueous dispersion with small-angle scattering

Solution structure and its relationship with the solid-state structure of poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonic acid) (PEDOT:PSS) determined the materials' conductivity and thus devices’ performance. In this work, we deciphered the multi-level structure of PEDOT:PSS with a set of sophisticated and complementary structural characterization techniques consisting of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS and SANS results disclosed that the PEDOT:PSS formed a conductive network in the aqueous dispersion, which was ascribed to a quaternary structure . Secondary doping with lithium bis(trifluoromethanesulfonyl)imide salt significantly changed the quaternary structure of PEDOT:PSS and thus enhanced the film conductivity. In addition, we studied in situ the change of quaternary structure and the sample resistance during solvent evaporation with SAXS and resistance measurements, respectively, which provided detailed and fundamental knowledge about the structure-property correlations. This fundamental knowledge would guide the design and preparation of advanced flexible electronics.