Poly(3-methylthiophene)-Based Counter Electrode for Electrochromic Windows

We propose a new poly-3-methylthiophene (PMeT)-based counter electrode, which is a series of arrays of PMeT-based material dots formed on a SnO ₂ substrate, and is virtually transparent in a visible region. The electrochromic window (ECW), tin oxide electrode (SnO₂:F)/tungsten oxide film/electrolyte/PMeT-based counter electrode, shows good electrochemical switching behavior, and electrochromic property. The function of the PMeT-based counter electrode is to reserve anions in the electrochromic reaction of the ECW, i.e., a supercapacitor. The behavior of the ECW was studied by a simple equivalent circuit. The EC cell fabricated with the PMeT-based counter electrode (PMeT-EC cell) yielded as large a differential optical density as that fabricated with a carbon-based counter electrode (carbon-EC cell), which we have already proposed, and the PMeT-based counter electrode had a higher capacitance per volume than a carbon-based counter electrode. The initial switching speed of the PMeT-EC cell was, however, slower than that of the carbon-EC cell, especially at lower temperatures. This is due to the fact that the activation energy of the PMeT doping process is higher than that of the carbon charging process.