Imparting High Conductivity to 3D Printed PEDOT:PSS

Complex 3D geometry and high conductivity have generally been mutually exclusive characteristics for conducting polymers. For instance, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a benchmark conducting polymer, typically exhibits conductivity 1 to 2 orders of magnitude lower in 3D-printed forms compared to 2D-processed thin films, due to its sensitivity to processing conditions. Here, we investigate the main causes of this reduced conductivity, which are found to be (1) the ink formulation strategy and (2) the strong lateral phase separation of the printed filaments. Processing approaches that overcome these factors have produced significant conductivity enhancement to 1200 S/cm, higher than the typical 2D-processed PEDOT:PSS. Our study also unveils a set of guiding principles for optimizing the conductivity of direct ink writing (DIW)-printed PEDOT:PSS, including printing orientation, print bed temperature, and nozzle diameter. With the combination of high conductivity and 3D geometric freedom, potential applications such as omnidirectionally deformable LED devices with strain-independent electrical behavior and bespoke electronics that replicate the shape of human body parts have been demonstrated.