3-oxetanylmethanol as additive to PEDOT:PSS for improved conductivity and water-resistance and applications in ink-jet printed electrochemical transistors

Abstract

3-oxetanylmethanol is used as additive to poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) water dispersions and the properties of thin films, prepared by spin-coating and ink-jet printing, either on glass or flexible polyethylene terephthalate (PET) substrates, are investigated. 1H NMR studies revealed that 3-oxetanylmethanol is reactive within the PEDOT:PSS medium during the film drying step at 120 °C, to form polyether compounds. Chemical cross-linking established through the esterification reaction of pendant hydroxyl groups in polyether chains, resulting from the 3-oxetanylmethanol in situ polymerization, and sulfonate groups from PSS, is also identified by the 1H NMR studies. Spin-cast films prepared from this formulation on either glass or PET exhibited electrical conductivity enhanced by more than two orders of magnitude, when compared to films obtained with the pristine PEDOT:PSS dispersion, reaching maximum values of around 596 and 682 Scm−1 for films on glass and PET, respectively, together with improved water-resistance. Atomic force microscopy and Raman spectroscopic studies, indicating that PEDOT chains are organized in more ordered domains in the films of the oxetane-based formulations, suggest that the polyether compounds modify the PEDOT:PSS phase segregation and promote charge transport across conducting PEDOT segments. Subsequently, improved conductivities and stability were also found for films prepared by high-resolution ink-jet printing of the formulations that led to the most conductive spin coated films. The potential application of the new ink formulations in printed electrodes interfacing aqueous media was assessed by ink-jet printing PEDOT-based electrochemical transistors operating with aqueous KCl electrolyte.