(233f) Ultrathin Plasmonic Coatings for Selective Radiative Transmission in Silica Aerogels

Current solar thermal collectors use vacuum insulation which only partially blocks outgoing infrared radiation from the absorbing surface. The losses associated with this phenomenon lead to a decrease in collector performance due to a reduction in temperature or efficiency. Visibly-transparent silica aerogels are a promising alternative to vacuum insulation in solar thermal applications. However, they are also characterized by undesirable transmission in the mid-infrared band. Here, we investigate ultrathin conformal plasmonic coatings to selectively enhance the absorption of silica aerogels in this target band and suppress outgoing radiative losses at high temperatures. We fabricated aerogels coated with aluminum-doped zinc oxide (AZO) using atomic-layer deposition (ALD). An evaluation of the microstructure via electron microscopy confirms that ALD is a suitable technique for the conformal coating of aerogels. Furthermore, we characterize the effect of the AZO coatings on the optical and thermal properties. We demonstrate AZO-coated aerogels with high solar transmission and low infrared transmission. The absorption coefficient in the target mid-infrared band increases substantially due to the AZO. In contrast, transmission of solar radiation through the materials was not significantly impacted. Ultrathin plasmonic coatings have the potential to significantly improve the performance of low-irradiance, high-temperature solar collectors.