Yuhao Zhang, Xinyu Li, Wenbo Wu, Yaru Zhang, Tifeng Jiao
Amidst intensifying energy crises, smart windows, which can automatically adjust light transmittance based on environmental conditions, have garnered significant attention as an energy-efficient technology. Hydrogels, with their unique optical transparency, stimulus responsiveness, and mechanical properties, have emerged as ideal materials for smart windows. This work elucidates the basic principles and significant features of hydrogels, such as their optical transparency, responsiveness to stimuli, mechanical attributes, and adaptability to different environments. It also explores their preparation techniques, which encompass chemical cross-linking, physical cross-linking, and dual cross-linking. It further discusses application examples of hydrogels in electrochromic, photochromic, thermochromic, humidity-responsive, and mechanochromic smart windows and summarizes the challenges faced in practical applications, such as material stability, optical performance, temperature response characteristics, and preparation costs. Future studies need to direct efforts toward optimizing materials and designing effective structures to produce cost-effective, high-performance hydrogels, thus promoting the further development and widespread application of smart window technology and providing new solutions for energy-saving and sustainable development in architecture.