Synergistic Doping of PEDOT:PSS via Methylammonium Iodide and Trifluoroacetic Acid for Highly Conductive Polymer Electrodes

Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is a widely used conducting polymer in organic electronics. Numerous doping strategies have been developed to enhance its electrical conductivity, most of which rely on secondary doping via acid-induced removal of the insulating PSS. However, these approaches often lack primary doping mechanisms that enrich charge carriers in the PEDOT chains. Herein, we propose a synergistic doping strategy that significantly enhances the conductivity of acid-treated PEDOT:PSS films by introducing methylammonium iodide (MAI) as a dopant. A simple one-step spin-coating of an MAI solution dissolved in trifluoroacetic acid (TFA) onto pristine PEDOT:PSS results in a dramatic increase in conductivity up to 1282 ± 90 S cm^–1 for a 39 nm film, compared to pristine (∼0.1 S cm^–1) and TFA-treated films (625 ± 29 S cm^–1). Comprehensive spectroscopic, morphological, structural, and theoretical analyses reveal that MAI facilitates PSS removal, promotes polaron formation in PEDOT, and stabilizes the doped structure. Furthermore, we demonstrate the practical applicability of MAI/TFA-treated PEDOT:PSS films as robust, high-performance electrodes in organic devices such as electrochromic devices exhibiting excellent operational stability.