Dynamic photothermal modulation in energy-efficient buildings

Energy-efficient buildings that optimize indoor and outdoor heat exchange, thereby reducing energy consumption have become a crucial solution for sustainable development. Among the primary heat exchange mechanisms between buildings and their surroundings, the propagation of thermal radiation is independent of the medium. The unique characteristic enables the effective regulation of indoor temperatures by modulating the photothermal properties of materials using the solar heat source and the outer space cold source. However, thermal radiation is influenced by many dynamic factors, posing significant challenges to material and device design. In response to this complex dynamic behavior, a series of photothermal modulation devices has been explored to achieve dynamic photothermal modulation, offering significant potential for improving energy efficiency in buildings. Here, we review recent advances in photothermal modulation technologies for key building components-windows, roofs, and walls-which play pivotal roles in regulating radiative heat exchange. We focus on the design principles, performance optimization strategies, latest advancements, and energy-saving effects of various device structures with photothermal modulation properties. The primary focus is on Fabry-Pérot (F-P) resonant cavity, thermochromic hydrogels, electrochromic devices, and mechanical flip devices . Notable achievements include thermochromic materials achieving excellent energy savings up to 200 MJ/m², electrochromic devices achieving optical modulation over 70 % in the visible spectrum, radiative cooling materials exhibiting high solar reflectance (>95 %) and mid-infrared emissivity (>0.9), as well as dynamic mechanical responsive systems displaying significant emissivity modulation up to 0.8. Finally, we discuss the challenges and future opportunities in photothermal modulation technology, offering insights into its transformative role in achieving sustainable and energy-efficient buildings. We believe this review will inspire further innovation and practical applications in the pursuit of sustainable energy-efficient building solutions.