A broadband-spectrally selective coating for building-integrated photovoltaic skylights cooling and building energy saving

With the widespread application of building integrated photovoltaic (BIPV)technologies in urban environments, there has been growing attention on how to maintain power generation efficiency (PCE) while passively reducing operating temperature. In this work, a broadband-spectrally selective coating (BSSC) for building BIPV skylights cooling and building energy saving was proposed, which composed of an outermost polydimethylsiloxane (PDMS) layer and a dielectric multilayer (DM) structure. The BSSC is designed to optimize BIPV skylights through the spectrally selective properties: (1) high above-bandgap (0.38–1.1 μm) transmittance (0.903) to ensure PCE; (2) high sub-bandgap (1.1–2.5 μm) reflectivity (0.353) to block solar radiation, and (3) high mid-infrared (4–25 μm) emissivity (0.956) to enable efficient radiative cooling. In the designed structure, the DM structure provides high above-bandgap transmissivity and sub-bandgap reflectivity, while the PDMS layer offers high MIR emissivity. Outdoor experimental results indicate that, when deployed as a skylight, the BSSC-coated glass reduces the indoor and floor temperatures by up to 3.9 °C and 8.7 °C, respectively, compared to uncoated glass. Meanwhile, when applied to retrofit the PV panel, it achieves a significant PV surface temperature reduction of 6.93 °C and indoor temperature reduction of 4.81 °C, at the cost of a 8 % decrease in power generation. Additionally, the BSSC exhibits an extraordinary building energy saving potential in most zones. This work provides a valuable reference for the thermal management of BIPV skylights, building energy saving and the design of multispectral metamaterial.