Solution-Processed Plasmonic–Dielectric Sunlight-Collecting Nanofilms for Solar Thermoelectric Application

It is important but remains a challenge to develop solution-processed plasmonic solar thermoelectricity films on various substrates, without strictly considering hierarchical plasmonic–dielectric–metal structures, to harvest a wide range of visible to near-infrared sunlight. We simply fabricate plasmonic silica metastructure sunlight-collecting nanofilms on highly reflective Cu and Si surfaces by introducing spin coating (with an Ag and silica colloidal mixture, a spin coater, and a heating plate) and low-temperature annealing (in an oven at 200 °C for 1 h) processes. The approximately 250 nm thick metastructure consists of a top 60 nm thick silica layer as an antireflective film and a bottom 190 nm thick Ag nanoparticle–silica hybrid film as a sunlight harvester. The metastructure film reduces the reflectivity of Cu (>90%) and Si (25–35%) to less than 5% at visible to near-infrared frequencies. The metastructure film on the Cu sheet has an absorptance of 0.95 and a thermal emittance of 0.06, ideal for high-performance sunlight absorbers. The solar thermoelectric powers of the film-coated Cu and Si are 15.4 and 4.7 times those of the uncoated Cu and Si substrates, respectively. The metastructure film on Cu exhibited a similar or slightly higher performance than that of a top-class vapor-deposited commercialized absorber film on Cu, demonstrating the robustness of the present method.