The impact of solvent doping on the morphology and performance of spray-coated PEDOT:dPSS: A USANS and SANS study

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is used in a broad range of organic electronics devices, where their performance can be dramatically enhanced by solvent processing. The morphological changes that occur with solvent processing, as well as the impact of deposition technique, are not well understood, but this understanding is crucial to rationally tune the performance of PEDOT:PSS. In this study, the change in the morphology and conductivity of spray-coated PEDOT:PSS films with pre- and post-deposition processing in the presence of polar solvents is investigated by means of neutron scattering. Deuterium labeling of PSS is used to distinguish between the PEDOT and PSS phases. Changes in the morphology of PEDOT:deuterated PSS (PEDOT:dPSS) films with the addition of 5% dimethyl sulfoxide (DMSO) to the pre-deposition PEDOT:dPSS solutions enhances the conductivity by ca. 60-fold, and is further enhanced by ca. 2-fold by soaking the films in ethylene glycol (EG). Neutron scattering reveals that the morphology of the spray-coated PEDOT:dPSS film consists of a two-phase structure on the micron to nanometer length scales, where more locally ordered PEDOT-rich fibril-like domains are dispersed on the smallest length scale. Upon DMSO addition, the PEDOT:dPSS domain sizes decrease dramatically. However, with soaking in EG, the sizes of the local domains increase isotropically. Thus, the enhanced electrical conductivity of the spray-coated PEDOT:dPSS with solvent doping is dominated by morphological changes, and not changes in the PEDOT:dPPS composition in these spray-coated films.