Noble-Metal-Free Sunlight Harvesting Meta-surface for Water Evaporation

Abstract

Abstract:We present ultrathin multilayer metamaterial absorbers based on abundant, low-cost materials, to effectively harness solar energy for heating and evaporation of water. We report on the design and experimental demonstration of ultrathin, broadband meta-surface absorbers for solar energy harvesting and conversion to heat in water for applications such as desalination, distillation, sterilization and purification. Structures are engineered to absorb >90% of incident light across a broad wavelength range from 300 to 1540 nm, and to concentrate this energy in the top 100 nm of the absorber where it can be efficiently transferred to water and thereby harnessed to accelerate evaporation.There is great and still growing interest in green energy sources that can reduce the collective energy footprint on the environment in the face of accelerating consumption. Solar energy harvesting is well known in the context of photovoltaic technologies but it may also be converted to heat and readily applied to the heating and evaporation of water for desalination, distillation, sterilization and purification, in particular where conventional power sources are unavailable. Such applications require not only an absorber covering as much as possible of the broad UV-NIR solar spectrum but one in which heat is generated and concentrated in a thin surface layer for efficient transfer to surrounding water. 'Perfect' metamaterial absorbers comprising metal/dielectric/nanostructured-metal tri-layers have become a familiar concept in recent years as the basis of resonant and wide-angle absorbers. These are typically based on noble metals, specifically gold and silver, for their strong, low-loss plasmonic properties in the VIS-NIR range but these are expensive metals and not well-suited to high absorption across the full UV-NIR solar spectrum. Here we present broadband meta-surface absorbers based on a low-cost, lossy metal (chromium) as opposed to the noble metals. Through a series of fully three-dimensional finite-element Maxwell solver simulations we evolved a five-layer absorber structure based on chromium (Cr), aluminum (Al) and silica (SiO 2 ) as shown in Fig.