Flexible smart photovoltaic foil for energy generation and conservation in buildings.

Building-integrated solar cells not only generate electricity but also impact the envelope thermal characteristics, thus changing the micro-climate of buildings. Therefore, the collective effects of energy conservation and generation on buildings should be considered in one design. In this work, a smart photovoltaic window foil with near-infrared (NIR) modulation and low long-wavelength IR emissivity has been fabricated by combining organic perovskite and inorganic tungsten doped vanadium dioxide nanoparticles (W-VO2 NPs). The W-VO2 offers solar modulation and promotes extraction and transport of photogenerated charges, giving peak power conversion efficiency of 15.4% at 25 ◦C and 16.1% at 45 ◦C and average visible transmission of 25.5%, comparable to the best reported semitransparent perovskite solar cell with an additional favorable NIR modulation of 10.7%. This new strategy to integrate energy-saving functionality into photovoltaic foil initiates a new design rule for smart window development.