In-depth exploration on the mechanism of various dopant ions on the infrared electrochromic characteristics based on poly(3,4-ethylenedioxythiophene) conducting polymers

Abstract

Abstract Poly(3,4-ethylenedioxythiophene) (PEDOT) is considered as an outstanding electrochromic material owing to its inherent infrared (IR) electrochromic properties, which has extensively application potential in intelligent IR thermal management. Although widespread studies concentrating on enhancing the IR electrochromic performances of PEDOT and much research showing that dopants significantly affect IR modulation, few experiments have deeply investigated the underlying mechanism. Herein, eight commonly dopantswere adopted to fabricate PEDOT film via in situ electrochemical deposition, and the IR electrochromic mechanism of PEDOT was further illuminated. Integrating Raman analyses, UV-Vis-NIR spectra, XPS analysis, FTIR spectra and DFT calculation, it is of significance to find that the generation and removal of polarons and bipolarons delocalized on PEDOT chains determine the reflectance regulation of PEDOT films. Where the positively polarized sulfur atoms in the thiophene rings can be viewed as the explicit manifestation of abstract polarons and bipolarons, i.e., charge carriers in the PEDOT chains. Additionally, the diverse IR control capabilities of various doped PEDOT devices are mainly resulted from the disparate charge carrier concentration of the oxidized state. Among the eight doped PEDOT devices, PSSNa-doped PEDOT owns the highest carrier concentration in the oxidized state and thus introduces the largest IR modulation amplitude of 0.566 in the wavelength scope of 3-5 μm.