Imaging the Phase Separation Between PEDOT and Polyelectrolytes\nDuring Processing of Highly Conductive PEDOT:PSS Films

Abstract

Treating PEDOT:PSS (Clevios) with\ncertain additives, such as ethylene glycol (EG), dimethyl sulfoxide\n(DMSO) and sorbitol, has been shown to increase the conductivity of\nthis material from roughly 1 to nearly 1000 S/cm. Using a slow drying\nmethod, we show that the additive induced a separation between free\nPSS and reorganized PEDOT:PSS complexes in the highly conductive PEDOT:PSS\nfilms. Additives (DMSO, DEG, and PEG 400) were included in PEDOT:PSS\naqueous dispersions at large volume fractions. The mixtures were slowly\ndried under room conditions. During drying, the evaporation of water\nresulted in an additive-rich solvent mixture from which the reorganized\nPEDOT:PSS complexes aggregated into a dense film while free PSS remained\nin the solution. Upon complete drying, PSS formed a transparent rim\nfilm around the conducting PEDOT film. The chemical compositions of\nthe two phases were studied using an infrared microscope. This removal\nof PSS resulted in more compact packing of PEDOT molecules, as confirmed\nby X-ray diffraction measurements. X-ray photoelectron spectroscopy\nand atomic force microscope measurements suggested the enrichment\nof PEDOT on the film surface after PSS separation. Through a simple\ndrying process in an additive-containing dispersion, the conductivity\nof PEDOT films increased from 0.1 to 200–400 S/cm. Through\nthis method, we confirmed the existence of two phases in additive-treated\nand highly conductive PEDOT:PSS films. The proper separation between\nPSS and PEDOT will be of relevance in designing strategies to process\nhigh-performance plastic electrodes.