2, Laboratoire de Physicochimie des Polymères et des Interfaces, Cergy, , France
Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is a potential candidate as a transparent soft conducting electrode for electronic and bio-electronic devices. It has also recently emerged as a potentially stretchable electrode when prepared under certain conditions. Despite a significant growth of the interest in this material, there is still significant debate about the causes and mechanisms involved in significant conductivity improvements in PEDOT:PSS films when processed in presence of certain additives, such as dimethylsulfoxide (DMSO) and Zonyl-FS300. Understanding the effects of these additives is crucial to further progress in the field, as it pertains to the design of even better electrode materials with finely tuned functionalities.
The addition of DMSO co-solvent significantly improved the conductivity and the carrier concentration by several orders of magnitude, as confirmed by Hall effect transport measurements. Addition of the Zonyl elastomer also improved the electrical properties, but to a slightly lesser extent. Importantly, it softens PEDOT:PSS significantly by reducing its Young’s modulus by more than an order of magnitude, making it increasingly stretchable and mechanically compliant. We show that these benefits can be combined to achieve excellent electrical, optical and mechanical properties. To understand the effect of these additives in isolation and in combination with each other, we have investigated the relationship between the transport properties of PEDOT:PSS and the morphology and microstructure of these films by performing atomic force microscopy (AFM) and grazing incidence wide-angle X-ray scattering (GIWAXS). Our analysis reveals distinctive impact of the two additives on the PEDOT and PSS components in the solid-state PEDOT:PSS films. The DMSO enhances the aggregation of PEDOT, while Zonyl introduces order into PSS domains. Both additives induce fibrillar formation in the film and the combination of the two additives only enhances the fibrillary nature and the aggregations of both PEDOT and PSS components of the film. In-situ GIWAXS investigation performed during the spin-coating and annealing steps showed that the presence of the additives influenced the aggregation behaviors of the PEDOT and PSS components directly during the transition from wet to dry film, i.e., during solvent removal, and do not evolve further during subsequent annealing. These results indicate that the additives directly influence the self-assembly behaviors of PEDOT and PSS during the ink-to-solid phase transformation.