Tunable wavelength selectivity of photonic metamaterials-based thermal devices.

Wavelength-selective thermal devices have great applications in concentrating solar power systems, high-temperature thermoelectric systems, and solar thermophotovoltaics (STPVs). Lack of high-temperature stability and spectrally selective emissivity in different wavelength regions limits their efficiency. We propose a one-dimensional HfO2/Al2O3-W nanocomposites/W/Al2O3/W multilayered photonic structure as potential wavelength selective thermal devices, and theoretically investigate the emission properties of the proposed Mie-resonance metamaterials from visible (VIS) to midinfrared (MIR) region. HfO2 thin layer is introduced to serve as an antireflection coating film and W layer acts as an IR reflection layer that enhances the absorptivity/emissivity in VIS and near-infrared (NIR) region while reducing the MIR emission simultaneously. Effects of geometric parameters are discussed, such as different radii and volume fractions of W nanoparticles, the thickness of Al2O3-W nanocomposites, and HfO2 thin film. The proposed thermal absorber and emitter exhibit nearly unity absorptance in both VIS and NIR regions, while the emittance approaches zero in the MIR region. The selective absorption/emission window is tunable by varying geometric parameters. The proposed solar thermal devices have great potentials in engineering applications such as STPVs and solar thermoelectric generator due to flexibility of geometric parameters and ease of fabrication.