Hollow photonic structures of transparent conducting oxide with selective and tunable absorptance

We adopted hollow 3D structures of transparent conducting oxides (TCO) for efficient emission control. TCO has high transmittance in the solar spectrum and tunable optical properties in the infrared regime due to their plasmonic property. The IR emissivity can be further adjusted by the geometry. Here, using solid and hollow triangles as an example, we modeled the spectral absorptance of 3D TCO structures with various carrier concentrations and geometrical factors. We showed that hollow triangular structures enhance the spectrally selective absorption, namely, high emittance in IR and low absorptance in the solar spectrum. This is because the large primary sizes of the triangles can interact strongly with the longer wavelength mid-IR while the small wall thickness of the hollow structures reduces the overall absorption volume for the shorter wavelength light in the near-IR and visible regimes. Further, by changing their angles, the hollow features can be used to tune the IR emissivity within a large range (from 0.14 to 0.8). The selective and tunable absorptance of 3D hollow structures of TCO may find applications in passive radiative cooling, solar thermal absorbing, and tunable windows glazing.