Synthesis of Linear Black Gold Nanostructures Processable as Sunlight and Low-Energy Light Collecting Films for Photo-Thermoelectricity.

As one of the effort to cope with the energy crisis and carbon neutrality, utilization of low-grade energy generated indoors (e.g., light) is imperative because this saves building and house energy, which accounts for ≈40% of total energy consumption. Although photovoltaic devices could contribute to energy savings, it is also necessary to harvest heat from indoor lights to generate electricity because the light absorbed by materials is mostly transformed into heat. For daily life uses, materials should not only have high absorptance and low emittance but also be easily processed into various forms. To this end, this work synthesizes black aqueous suspensions containing winding and bent linear gold nanostructures with diameters of 3-5 nm and length-to-diameter ratios of ≈4-10. Their optical and photo-thermal characteristics are understood through experimental and theoretical investigations. Black gold nanostructures are conveniently processed into metal-dielectric films on metal, glass, and flexible substrates. The film on copper has an absorptance of 0.97 and an emittance of 0.08. Under simulated sunlight and indoor LED light illumination, the film has equivalent photo-thermal and photo-thermoelectric performances to a top-tier sunlight-collecting film. This work attempts to modify the film structure to generate more usable electricity from low-energy indoor light.