Enhancing thermal comfort and photovoltaic efficiency through thermotropic starch–hydrogel composite membrane integration in sustainable building fenestration

This study develops a transparent, biocompatible hydrogel membrane (HGM) for sustainable building fenestration. Made from hydroxypropyl cellulose, poly(acrylic acid), and starch derived from waste potato peels, the HGM leverages bio-waste valorization. It exhibits thermotropic behavior, dynamically adjusting optical transparency with temperature. Extensive physicochemical analyses confirmed the molecular interactions governing its optical and thermal properties. When incorporated into a prototype double-glazed window, the HGM significantly enhanced indoor thermal regulation, achieving a low thermal conductivity at 0.23 W m−1 K−1 and thermal transmittance (U-value) of 1.84 W m−2 K−1 and effectively mitigating temperature differentials of up to 30 °C. The synthesized hydrogel exhibits a tunable transition temperature, high luminous transmittance of 72%, notable solar modulation efficiency of 75%, and exceptional durability. In addition to thermal performance, the HGM improved the efficiency of the underlying silicon photovoltaic cell by up to 15% compared with its standalone performance. This enhancement is attributed to the presence of light-scattering centers within the HGM, which facilitate total internal reflection and contribute to thermal buffering. Functioning dually as a passive radiative cooling layer and an optical modulator, the HGM material demonstrates multifunctionality tailored for building-integrated photovoltaic systems. This study advances the domain of energy-efficient architecture by integrating sustainable materials with improved solar and thermal regulation properties, thereby promoting the development of climate-responsive building designs.