Field-Enhanced Near-Infrared Reflector (NIR) as Smart Glass for Solar Panels

Abstract

Solar panels are ensembles of solar cells that convert solar light into electricity. During the operation, the temperature of the solar panel can reach as much as 900C. With each degree centigrade the conversion efficiency of the solar generator decreases by 0.46%. Thus, in a hot summer day, the power generated can decrease by as much as 30%.

Therefore the development of a versatile and robust, metamaterial that can reflect near infrared heat radiation (NIR) in the range 0.7-2.5 μm while transmitting more than 90% of the visible light intensity is highly desirable. Metal oxides can be used to manage the light reflectance over the long wavelength range. However, to obtain high reflectivity starting at shorter wavelengths, the doping concentration of the metal oxide has to be increased above the level of 1x1021/cm3. At these concentrations the dopant incorporates not only substitutionally but large amounts will also be found interstitially. Interstitial dopants have been shown to produce carriers with heavier effective mass, decreased mobility, and deeper donor states that significantly decrease the transmittance. Ultimately substitutional dopants degrade the crystallinity of the host material, generating compensating defects that limit the achievable carrier density.

The metamaterial that we propose is a robust, thin film structure that has the ability to reflect near infrared heat radiation (NIR) with λ>1.1 μm while transmitting more than 90% of the visible light intensity. To circumvent the need for excessive dopant incorporation we have designed a structure that alternates insulating and conducting layers of silicon dioxide (SiO2) and silicon doped zinc oxide film (ZnO:Si). This structure is deposited by magnetron sputtering from Si and ZnO targets at low temperature. The ability to reflect NIR and transmit selected wavelength rage is obtained through the field-enhanced electron concentration of the moderately doped ZnO thin film at the dielectric/ZnO:Si interface.

Solar panel’s glass covered with this thin film can achieve the radiative cooling of the solar cells without interfering with the conversion into electricity of the photons with wavelengths shorter than 1.1 μm.