Abstract:
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.
