Optical and electrical responses of polymeric electrochromic devices: effect of polyacid incorporation in polyaniline film

Solid electrochromic devices (ECDs) are prepared with chemically deposited electroactive polyaniline (PANI) and PANI-poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) thin films. The analysis of their electrical current responses suggests a higher redox potential value of the unmodified PANI thin film compared to that of the PANI-PAMPS ECD. Optical transmittance spectra of the devices show that the polyacid incorporation in PANI thin films reduces the switching voltage from ±2 to ±1.5 V, increases the optical contrast ratio by 10% at around 650 nm and doubles the optical response rate of the devices using LiClO4 dissolved in polymethyl methacrylate (PMMA) as a solid electrolyte. A parametrical analysis of the optical kinetic curves, together with the Butler–Volmer equation, indicates that PANI films contain two kinetically different phases: an interconnected network on which electrical conduction is predominated by percolation and a diffusion-controlled charge transfer zone. The first one contributes to the faster term and the second one to the slower term of the polymeric ECD optical responses.