ABSTRACT:In this work, a metamaterial selective solar absorber made of nanostructured titanium gratings deposited on an ultrathin MgF 2 spacer and a tungsten ground film is proposed and experimentally demonstrated. Normal absorptance of the fabricated solar absorber is characterized to be higher than 90% in the UV, visible and, near infrared (IR) regime, while the mid-IR emittance is around 20%. The high broadband absorption in the solar spectrum is realized by the excitation of surface plasmon and magnetic polariton resonances, while the low mid-IR emittance is due to the highly reflective nature of the metallic components. Further directional and polarized reflectance measurements show wide-angle and polarization-insensitive high absorption within solar spectrum. Temperature-dependent spectroscopic characterization indicates that the optical properties barely change at elevated temperatures up to 350°C. The solar-to-heat conversion efficiency with the fabricated metamaterial solar absorber is predicted to be 78% at 100°C without optical concentration or 80% at 400°C with 25 suns, and could be further improved with better fabrication processes and geometric optimization during metamaterial design. The strong spectral selectivity, favorable diffuse-like behavior, and excellent thermal stability make the metamaterial selective absorber promising for significantly enhancing solar thermal energy harvesting in various system at mid to high temperatures.

color-tunable semitransparent perovskite solar cells for building-integrated photovoltaics.

Here we demonstrate a new route to achieve the sintering of silver nanoparticles (Ag NPs) at room temperature. The as-prepared Ag NPs coalesced when they were immersed in electrolyte solutions, such as NaCl and MgSO 4 . The square resistances of Ag NPs thin films decreased from tens of kiloohms to lower than 1 ohm after treatment with electrolyte solutions for 10 s. Conductive Ag NPs thin films can be created on various substrates coated by polydopamine, a mussel-inspired polymer, via silver-plating followed by treatment with electrolyte solutions at room temperature. Experimental Fabrication of the polydopamine coating on substratesCommercially available glass, SiO 2 ceramics, polypropylene (PP), poly(ethylene terephthalate) (PET), silicon wafer, poly