Variable infrared emittance mechanisms of electrochromic film based on poly(aniline) under various doping concentrations of camphorsulfonic acid

Poly (aniline) (PANI) is considered an ideal material for the modulation of infrared (IR) radiation due to its excellent electrochromic properties. However, the camphorsulfonic acid doping mechanism which results in emittance modulation is not clearly understood. With the goal of enhancing the IR emittance variation (Δε), a PANI film was synthesized by a chemical oxidation and spraying method, and the doping mechanism of CSA concentration effect on Δε was studied by combining Raman spectra, X-ray photoelectron spectra and density functional theory calculations. The results demonstrate that with increasing camphorsulfonic acid concentration, the effect of the doping concentration on the emittance of PANI/Au films can be divided into two stages: (1) the change in the emittance is mainly caused by the shortening of optical penetration depth either under the state of dopant free (non-doped) or a low CSA doping concentration; (2) the change in emittance is mainly caused by the increase in reflectivity of the PANI layer under the increased doping. Due to the joint action of the two factors, the emittance of the PANI film first increases and then decreases with increasing concentration of CSA, and the maximum Δε (0.45) is realized at 1 M. This paper clarifies the mechanism of PANI films with different CSA dopant concentrations and could provide a way to increase the emittance modulation range by adjusting the concentration of the dopants.