Adaptive photonic films for fenestration-integrated PV technology to enhance energy saving and thermal comfort: Concept and theoretical investigation

Photovoltaic (PV) fenestration is a widely adopted building-integrated PV technology. However, its application often results in indoor overheating during summer daytime and overcooling during winter nighttime. Traditional thermal insulation solutions are expensive to retrofit and fail to harness the potential energy benefits from the sky. To address these challenges, this study proposes and numerically investigates adaptive glass films based on VO₂ photonic coatings for retrofitting existing PV fenestrations. The microstructure of the coating is designed and optimized using the transfer matrix method coupled with the effective medium model. The optimization results suggest that the cooling film has emissivity of about 0.44 during daytime and 0.86 at night, while the heating film has emissivity of about 0.68 during daytime and 0.26 at night. The thermal performance of PV fenestrations equipped with the optimized films is evaluated in a region with hot summers and cold winters. The simulation results indicate that the time percentage within the thermal comfort range could increase by approximately 0.6–2.5% in summer and 0.9–35.2% in winter, depending on the PV coverage ratio and tilt angle. In buildings with temperature and thermal comfort controls, the photonic coatings per unit area are predicted to yield annual electricity savings in the range of approximately 36.5–53.5 kWh and 45.1–63.0 kWh, respectively. This study proposes a conceptual solution to enhance the thermal performance of buildings integrating PV technology and provides simulation-based projections of its potential energy and comfort benefits. © 2026 Elsevier Ltd.