Highly Durable Electrochromic Devices for More than 100,000 Cycles with Fe(II)-Based Metallo-Supramolecular Polymer by Optimization of the Device Conditions

An electrochromic device (ECD) with a stable and durable optical transition between color and bleached state is the primary demand for future commercialization. When an EC smart window is installed in buildings or vehicles and turned ON or OFF 10 times per day, the ECD needs to be stable for at least 100,000 cycles to have a 30-year lifespan. Herein, a solid-state ECD of an Fe(II)-based metallo-supramolecular polymer (polyFe) with excellent durability was fabricated by incorporating nickel hexacyanoferrate (NiHCF) as a charge-balancing layer. The solid-state ECD displayed bleaching and coloring at +1.0 and +0.2 V, respectively, with maximum optical contrast of greater than 60%. The minimalization of the potential difference during EC changes enabled ultrahigh cycle stability and improved optical memory. For the further improvement of the EC properties, it was revealed that the optimization of the film thickness of the polyFe and NiHCF is critical to maintaining the charge balance between the working and counter electrodes. At last, cyclic stability for repeated color changes over 100,000 cycles was achieved.