Photoelectrochromic devices based on cobalt complex electrolytes

In this paper, a photoelectrochromic device (PECD) composed of a conducting polymer electrochromic electrode and a ruthenium-based dye-sensitized TiO2 nanoparticle electrode is constructed and investigated. Three cobalt complexes, which are [Co(bpy)(3)](n+), [Co(phen)(3)](n+) and[Co(NO2-phen)(3)](n+), are introduced into the PECD as the redox couples and a self-powered coloring/bleaching process of the cobalt electrolyte-based PECDs is achieved for the first time. The PECD using the [Co(NO2-phen)(3)](n+) electrolyte presents the highest transmittance modulation of 42.6% at 636 nm between the colored and bleached states. From current-voltage characteristics, it is found that the transmittance of bleached PECD is improved with a higher open-circuit voltage, resulting in an enhanced transmittance modulation. Electrochemical impedance spectroscopy (EIS) studies indicate that the charge transfer resistance (R-ct) at PProDOT-Me-2 vertical bar electrolyte interface is correlated with the response time for the bleaching process.