Color-to-white switching electrochromic devices constructed by combining fused thienothiophene polymers and high-reflectivity electrolyte†

Color-to-white switching electrochromic devices (ECDs) present great application potential in non-emissive displays and energy-saving fields, but there are still very few reports. In this work, three fused thienothiophene polymers are synthesized via direct arylation polymerization (DArP), and the optical absorption is tuned by incorporating different embedded units into the fused thienothiophene mainchain. The resultant polymers demonstrate good electrochromic properties such as high optical contrast, fast switching response and good stability, and are also highly transmissive in the oxidized state. Additionally, a quasi-solid white electrolyte with a reflectivity of 75%, ionic conductivity of 8.1× 10⁻⁶ S cm⁻¹ and mechanical strength of 1.33 MPa is prepared by optimizing the composition of the polymer, TiO₂, and ion liquid. Then, three color-to-white electrochromic devices (ECDs) are successfully fabricated by combining the synthesized polymers and the white electrolyte, and also present good electrochromic properties such as high optical contrast, fast switching response, good stability, etc.