Direct Ink writing of high conductive PEDOT:PSS dispersion with an engineered conformation and electronic structure for printed electronic circuits†

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a widely used electro-active conjugated polymer, is a good candidate for printed electronics owing to its advantages of solution processability and remarkable stability under oxygen conditions. However, achieving high conductivity is still a challenge in this field. Most previous studies have focused on the improvement of electrical conductivity of PEDOT via post-treatment of commercially available PEDOT:PSS. From another point of view, this work represents the enhancement in charge carrier transport by controlling polymerization parameters, i.e., oxidizing agent concentration and polymerization temperature. Thus, 2.25 equivalents of APS per mole of EDOT and 10 °C were found to be the optimum conditions. These produced PEDOT chains (with a low band gap energy, high oxidation state, quinoid structure and low molecular weights, along with the formation of enhanced fibrous PEDOT-rich domains in the solid state) enhanced electrical conductivity of the prepared PEDOT:PSS aqueous dispersion up to 165 S cm⁻¹. After solvent post-treatment of the optimum PEDOT:PSS dispersion, electrical conductivity increased up to 1410 S cm⁻¹, and this is the highest conductivity reported for post-treated PEDOT:PSS dispersions thus far. Finally, the obtained PEDOT:PSS dispersion was successfully formulated as a surfactant-free conductive ink for printing a three-layered circuit on a flexible substrate with a conductivity of 1800 S cm⁻¹ and lightening up an LED lamp using a direct ink writing (DIW) technique.