Modulation of optical properties of electrochromic device

An experimental investigation is carried out to modulate the optical properties of electrochromic devices (ECD) by varying the thickness of electrochromic polymer (ECP) layer. Polyaniline (PANI) is preferred as ECP due to its ability to change colors from light green to green to blue at different voltages. ECDs are fabricated having varying thickness (250–650 nm) of the PANI layer. Topography, morphology, and optical measurements show that the roughness, porosity, and shade of green color depend on the thickness of PANI layer. The effect of ECP layer thickness on the optical performance of ECDs is evaluated through detailed electrochemical, optical, spectroelectrochemical measurements, and spectral colorimetry. ECD shows different shades of green and blue color with higher color contrast for the thicker PANI layer. It is attributed to the roughness and porosity-induced multiple scattering and trapping of incident light in the ECP layer. The reflectance spectra are later used to define the color space for all the ECDs. While the color difference of the ECD fabricated with 250-nm-thick ECP is small, the ECDs prepared using thicker ECP layers show noticeable color difference of greater than 2. Finally, it is shown that varying PANI-based ECP layer thickness is a feasible strategy to modulate the shade of green color in ECDs.