An All-Weather Sol-Gel Thermochromic Energy-Saving Smart Window

Thermochromic smart windows achieve energy conservation and emission reduction by regulating the energy exchange in buildings. However, their widespread application in architecture has been hindered by issues such as poor frost resistance, limited durability, high costs, recycling challenges, and suitability only for specific climates (such as tropical climates). To address these challenges, we have successfully developed a high-performance thermochromic window, which is an intelligent window based on a thermochromic solution of poly(vinyl alcohol) acetal and LiCl, encapsulated in a glass/thermal liquid/low-E structure. This thermochromic window exhibits scalability, frost-resistance, durability and all-climate adaptability (referred to as SFDA window, with the thermochromic liquid termed SFDA liquid). First, the SFDA liquid reported here utilizes an efficient one-pot aqueous synthesis technique to directly produce a polyvinyl acetal solution. This process not only supports large-scale production but also incorporates LiCl in situ, endowing the liquid with excellent frost resistance. Second, the concentration is purposefully adjusted to the entangled concentration to facilitate the sol-gel transition, ensuring durability during long-term use. Additionally, windows containing SFDA liquid demonstrate excellent performance, maintaining up to approximately 84% light transmittance and 70.7% solar radiation at 20 °C. Third, our SFDA window achieves high-efficiency energy savings compared to traditional thermochromic windows across all-weather conditions. Through indoor simulations, we found that SFDA window can cut energy consumption by 64.6% relative to traditional glass windows in the summer. In the winter, compared to traditional glass windows, windows containing SFDA liquid can reduce heating energy consumption by 52.3%. In simulations conducted across 33 cities worldwide, SFDA liquid windows achieved a total monthly energy savings of 1179.8 MWh compared to commercial Low-E window. With its outstanding energy efficiency, the SFDA smart window opens up a brand-new development pathway in the field of green economy.