Broadband Meta-Absorber with Au/Ni Core–Shell Nanowires for Solar Vapor Generator

Solar energy has the advantages of being eco-friendly, practically infinite, and nonreliant on chemical fuels. A solar vapor generator uses sunlight to transform a liquid stream into a vapor stream to operate a turbine for generating electricity. For efficient vapor generation, it should absorb the sunlight in broad spectrum with high absorption, and also have high photothermal conversion efficiency. In this work, Ni nanowires and Au/Ni core–shell nanowire absorbers which meet the relevant conditions are fabricated using a cost-effective process for efficient solar vapor generation. The light is scattered and trapped in the nanowires and the electrical field is enhanced between the nanowires by the surface plasmonic gap resonance, resulting in high absorption. Also, the adiabatic nanofocusing structure generates heat at hot spots, resulting in efficient photothermal conversion. As a result, the Ni and Au/Ni core–shell nanowire absorbers respectively, absorb over 98% and 91% of the incident light in the solar spectrum. Further, the efficiency of photothermal conversion of the Au–Ni absorber under 1 Sun is found to be ≈33%. These absorbers have the potential to be applied to diverse fields, such as desalination, solar thermophotovoltaics, and metamaterials.