Beyond acid treatment of PEDOT:PSS: decoding mechanisms of electrical conductivity enhancement

Abstract

Despite widespread recognition of acid treatment as a crucial method for enhancing electrical conductivity and expanding the applications of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), the mechanisms behind this improvement are yet under debate. In this study, we delved into the impact of various acids, including H₂SO₄, H₃PO₄, HCl, and HCOOH, on the electrical conductivity and structural alterations of PEDOT:PSS thick films (∼5 μm). Our findings demonstrate a robust correlation between high electrical conductivity and well-developed crystallinity. The high degree of crystallinity originates from a densely packed and well-ordered structure, which is remarkably influenced by the inter-lamellar stacking distance and the alignment of PEDOT lamella along the edge-on direction. Notably, through the combination of acid treatment and hot-pressing techniques, we achieved a remarkable enhancement in the electrical conductivity of PEDOT:PSS thick films, setting a new record of 3360 S cm⁻¹. These films also exhibit remarkable properties, including high bending flexibility and tensile strength (42 MPa). As a result, the resultant strong, flexible, and highly conductive films can be used for high-end electromagnetic interference (EMI) shielding applications where it presented a high EMI shielding effectiveness and specific EMI shielding effectiveness of 51.79 dB and 75057.97 dB cm² g⁻¹ at a thickness of 4.66 μm, respectively.