Solar Harvesting and Regulating Windows for Energy-efficient Buildings 

Buildings account for more than 40% of global energy consumption. Energy-efficient components have been integrated into buildings for reducing energy consumption, among which smart windows are promising candidates. Smart windows are mostly designed based on sunlight transmission regulation, which allow full solar spectrum into the room for indoor heating in the winter, while, in the summer, allow visible light in for indoor lighting and reject ultraviolet and near-infrared to reduce the energy consumption for indoor cooling. However, rejection of ultraviolet and near-infrared dissipates around 56% of solar energy into waste heat and intensifies the urban heat island effect. Therefore, it is expected that, by harvesting the ultraviolet and near-infrared and converting them into thermal energy or electricity, building efficiency will be improved and urban heat island effect will be minimized. However, concurrently harvesting ultraviolet and near-infrared and transmitting visible light require a window to possess a complicated solar spectrum selectivity, which is highly challenging for present window systems. To tackle this challenge, we will design and develop a multicomponent and multifunctional window to achieve the solar spectrum selectivity. The work will be implemented from two progressive levels:material-engineering levelandsystem-integrating level. At the material-engineering level: to harvest ultraviolet, we will use a transparent photovoltaic cell to generate electricity and transmit visible light and near-infrared; to harvest near-infrared, we will develop a transparent selective solar absorber to convert near-infrared into thermal energy and transmit visible light. Specifically, we will engineer cesium-doped tungsten trioxide nanoparticles as a transparent solar absorber and an underlying silver nanowire layer as a mid-infrared reflection layer (to obtain low mid-infrared emissivity).At the system-integrating level, we will fabricate a window prototype by assembling the transparent photovoltaic cell and transparent solar absorber, followed by evaluating the solar energy harvesting performance through measuring electrical generation and thermal energy production. We will assess the solar regulating performance through measuring the thermal insulation value and solar heat gain coefficient in a thermal transmittance experiment. Next, we will build an electrical-thermal coupled model to calculate annual solar energy harvesting data, which will be further coupled with a building energy simulation to calculate the annual building energy savings. Our proposed research is the first systematic attempt to integrate transparent photovoltaic cell and transparent solar absorber into a window. We expect the results from this project will provide both scientific inspirations and practical solutions to present green building technologies.