Collaborative Research: Solar Energy Harvesting, Photothermal-Photovoltaic Dual Modality Building Skins towards Energy Neutral Civil Structures

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Residential and commercial buildings account for 40 percent of the total energy consumption in the United States. New concepts at the intersection of materials science and architectural and civil engineering present opportunities to achieve highly energy-efficient buildings. A building skin has been conventionally considered as a weather-resistive barrier. This research offers to transform the building skin to an active system capable of harvesting sunlight with varying energy outputs according to seasonal changes. This is achieved by applying nanoscale thin films to building skins that are multifunctional and active for energy harvesting, conversion, and utilization. Glass-based high-rise building skins provide the ideal material for applying the energy harvesting nanoscale thin films. The thin films will be engineered to offer two major functions, where photovoltaic or photothermal effects are switched alternatively depending on seasonal needs. In summer, the photovoltaic effect is used to transform the solar energy to electricity for building use. In winter, the solar energy is converted to heat to reduce heat loss in the buildings. This research will lead to transformative impacts towards achieving energy-neutral civil infrastructure. Educational programs will be established for K-12 and underrepresented minority outreach.The goal of this research is to develop a multifunctional building skin capable of efficient solar harvesting for dual modality energy outputs (thermal or electric) controlled based on seasons. Principally, both photothermal and photovoltaic films share the same optical characteristics: strong UV/NIR absorptions with high visible transmittance, the only difference is the form of energy output. Compared with multi-pane glazing, single-panes are practically not viable due to rapid heat transfer through building skin. If a spectral-selective thin film is applied on a window surface, the skin surface temperature can be increased from 25 °C to 50 °C via the photothermal effect. This effectively reduces thermal energy loss from the interior. In this way, thermal insulation can be achieved optically without intervention medium. On the other hand, the undesirable solar infrared in summer can be compensated by the same thin film but in a different modality: photovoltaic. Absorption of large infrared irradiation not only reduces cooling energy but generates electricity for other appliances. Fundamental mechanisms will be investigated on the relationship between spectral selectivity and nanostructures that enable the most efficient energy harvesting and conversion.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.