Electrochemical investigation of PEDOT films deposited via CVD for electrochromic applications

A patterned solid-state electrochromic device on an ITO-coated plastic substrate was demonstrated that incorporates poly-3,4-ethylenedioxythiophene (PEDOT) deposited via a solventless oxidative chemical vapor deposition (oCVD) technique. In this paper, we present a thin-film electrochemical and optical analysis of oCVD PEDOT. oCVD PEDOT films about 100 nm thick on ITO/glass had optical switching speeds of 13 and 8.5 s, for light-to-dark and dark-to-light transitions, respectively. The color contrast was 45% at 566 nm and is 85% stable over 150 redox cycles. An Anson plot indicates that oCVD PEDOT color transition speeds are limited by ion diffusion rates, rather than electron or hole conductivity. Dimensionless analysis predicts gains of up to in oCVD PEDOT redox switching speeds by reducing the film thickness an order of magnitude to 10 nm. oCVD is a temperature-controlled process capable of conformal conductive polymer depositions onto a range of substrates from the vapor phase. Compatible substrates include plastic, paper and fabric. Non-conductive dispersion additives are not needed with oCVD, eliminating a potential source of defect-causing corrosion. oCVD offers powerful capabilities that may overlap with key challenges for the designers and fabricators of organic thin-film electronics, including OLED lighting and displays, electrochromics, photovoltaics, and semiconductors.