High-contrast electrochromic coatings and devices for health assurance, visual comfort and energy-saving in buildings

High-contrast electrochromic coatings and devices reduce the ultraviolet-radiation from sunlight, ensure human health and visual comfort, save the electricity consumption of the heater in winter, and save electricity consumption of air conditioners in summer. Anodically coloring polymer coatings (P(CDBP), P(CDBP-co-BTPH), P(CDBP-co-TFU), P(CDBP-co-CDT) and P(CDBP-co-CDTK)) based on 4,4′-bis(carbazol-9-yl)-2,2′-dimethylbiphenyl (CDBP) and four different dithiophene derivatives (2,2′-bithiophene (BTPH), 2-(2-thienyl)furan (TFU), 4H-cyclopenta[2,1-b:3,4-b’]dithiophene (CDT), and cyclopentadithiophene ketone (CDTK)) are polymerized electrochemically on ITO electrode. The P(CDBP-co-BTPH) electrochromic coating has high transmittance change (ΔT = 71.1 %) and coloration efficiency (160.6 cm² C⁻¹). P(CDBP-co-BTPH) film reveals yellow-gray and dark blue in neutral and oxidation states, respectively. Electrochromic energy saving devices (ECDs) are assembled using P(CDBP), P(CDBP-co-BTPH), P(CDBP-co-TFU), P(CDBP-co-CDT) and P(CDBP-co-CDTK) films as the anodic layers and poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PPD-M2) film as the cathodic layer. P(CDBP-co-BTPH)/PPD-M2 ECD shows a high transmittance change (ΔT = 30.3 %) and a rapid response time (≤0.3 s). Moreover, P(CDBP-co-BTPH)/PPD-M2 ECD also has sufficient optical memory and redox cycling stability. These findings provide us new insights for the useful design of polymer coatings in rapid switching electrochromic energy-saving devices and switchable architectural windows.