Systematic prediction of maximum electrochromic contrast of an electrochromic material

When reporting electrochomic (EC) properties, it is required to give a quantitative measure of the intensity of the color change. Even though the transmittance difference (ΔT) between the two states has been used widely, many researchers tend to find out the maximum EC contrast (ΔTmax) and the corresponding thickness (Lm) of an EC material on a trial-and-error basis. In this article, we propose a very convenient and systematic method to predict the ΔTmax and the Lm of an electrochromic material. These quantities are material characteristics, which are independent of the device. In order to demonstrate the usefulness of the method, we carried out EC experiments using a well-known EC polymer, poly(3,4-ethylenedioxythiophene) [PEDOT]. PEDOT was prepared by electropolymerization of the corresponding monomer in a potentiodynamic mode. The film thickness was controlled by varying number of sweep cycles. The ΔTmax of PEDOT was estimated to be 48.2% at ca. 3 cycles in the case of 0.02 M PEDOT solution. We believe that the systematic approach can also be applied to variety of coating processes in the EC device fabrication.