Thermoplasmonic Nanorings for Passive Solar‐Responsive Smart Windows in Energy‐Efficient Building Applications

Abstract Reducing solar heat gain through windows is a major challenge in the pursuit of energy‐efficient buildings. Current smart window technologies aim to modulate near‐infrared (NIR) solar transmission suffering from limitations in transparency, responsiveness, and long‐term stability. Here an approach based on thermoplasmonic effects are presented to dynamically regulate NIR light transmission in a passive and energy‐free manner while retaining transparency. Silver nanorings (200nm diameter) with NIR resonances are integrated into a double‐glazed format and used as local heat sources via solar photon‐thermal conversion to drive reversible evaporation of a liquid overlayer. The resultant fast dynamic shift in the local refractive index moved the NIR resonances to shorter wavelength in real‐time providing a larger overlap with the solar spectrum at higher solar intensities. NIR blocking is demonstrated as the solar intensity varies across the day changes allowing heat transmission in early morning and late afternoon but progressively blocking toward midday. Dynamic blocking translates into a >4°C reduction in interior temperature while maintaining transparency in the visible region with a passive solution not requiring an external electric input. These findings position nanorings as promising materials for next‐generation smart windows, offering dynamic spectral blocking, environmental responsiveness, and compatibility with large‐area fabrication techniques.