Three‐Mode Modulation Electrochromic Device with High Energy Efficiency for Windows of Buildings Located in Continental Climatic Regions

Abstract A sustainable use of energy in buildings demands energy‐efficient windows. A new design concept for electrochromic (EC) smart windows, easy to implement at the industrial level, is introduced here. It enables simultaneous control of visible and near‐infrared (NIR) solar radiation, thus contributing to reduce heating and cooling loads especially in buildings located in areas experiencing wide daily temperature ranges. The EC device comprises amorphous indium zinc oxide, a conducting oxide transparent in the visible and NIR spectral regions, as nonactive layer, and a sol–gel protonic ionic liquid‐doped di‐ureasil electrolyte displaying high transparency and proton conductivity. The device offers three voltage‐operated modes: bright hot (+3.0 V: transmittances of 70/83% at 555/1000 nm), semi‐bright warm (−2.0 V: transmittances of 37/35% at 555/1000 nm), and dark cold (−2.5 V: transmittances of 6/4% at 555/1000 nm). Its main figures of merit are: high switching efficiency (transmittance variations of 64/79% at 555/1000 nm), high optical density modulation (1.1/1.3 at 555/1000 nm), high optical contrast ratio in the visible region (lightness variation of ≈43), good cycling stability, and unprecedented coloration efficiency (−12538/−14818 cm² C⁻¹ and +2901/+3428 cm² C⁻¹ at 555/1000 nm), outstanding optical memory (transmittance variation loss of only 24% more than 4 months after coloration), and self‐healing ability following mechanical stress.