In-Depth Exploration of the Mechanism by which Various Dopant Ions Affect the Infrared Electrochromic Characteristics of Poly(3,4-ethylenedioxythiophene) Conducting Polymers

Poly(3,4-ethylenedioxythiophene) (PEDOT) is considered an outstanding electrochromic material owing to its inherent infrared (IR) electrochromic properties, which have extensive application potential in intelligent IR thermal management. Although widespread studies concentrate on enhancing the IR electrochromic performances of PEDOT and much research shows that dopants significantly affect IR modulation, few experiments have deeply investigated the underlying mechanism. Herein, eight common dopants were adopted to fabricate PEDOT film via in situ electrochemical deposition, and the explicit manifestation of abstract charge carriers which determines the IR electrochromicsm of PEDOT was further illuminated. Integrating Raman analyses, UV–vis–NIR spectra, XPS analyses, FTIR spectra, and DFT calculation, it is of significance to find that the polarons and bipolarons delocalized on PEDOT chains are related to the positively polarized sulfur atoms in the thiophene rings, the intensity variations of which decide the reflectance regulation of PEDOT films. Additionally, the diverse IR control capabilities of various doped PEDOT devices mainly result from the disparate charge carrier concentration of the oxidized state. Among the eight doped PEDOT devices, PSSNa-doped PEDOT has 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.