Thermochromic hydrogel-based energy efficient smart windows: fabrication, mechanisms, and advancements

Thermochromic smart windows are regarded as highly cost-effective and easily implementable strategies with zero energy input among the smart window technologies. They possess the capability to spontaneously adjust between transparent and opaque states according to the ambient temperatures, which is essential for energy-efficient buildings. Recently, thermochromic smart windows based on hydrogels with various chromic mechanisms have emerged to meet the increasing demand for energy-saving smart windows. This review provides an overview of recent advancements in hydrogel-based thermochromic smart windows, focusing on fabrication strategies, chromic mechanisms, and improvements in responsiveness, stability and energy-saving performance. Key developments include dual-responsiveness, tunable critical transition temperatures, freezing resistance, and integrations with radiative cooling/power generation technologies. Finally, we also offer a perspective on the future development of thermochromic smart windows utilizing hydrogels. We hope that this review will enhance the understanding of the chromic mechanism of thermochromic hydrogels, and bring new insights and inspirations on the further design and development of thermochromic hydrogels and derived smart windows.