Spectrally selective coatings for optical surfaces
Techniques, systems, devices and materials are disclosed for spectrally selective coatings for optical surfaces having high solar absorptivity, low infrared emissivity, and strong durability at elevated temperatures. In one aspect, a spectrally selective coating includes a substrate formed of a light absorbing material, and a composite material formed over the substrate and including nanoparticles dispersed in a dielectric material, in which the composite material forms a coating capable of absorbing solar energy in a selected spectrum and reflecting the solar energy in another selected spectrum.
1. A method of fabricating a spectrally selective coating, comprising:
producing, by a spark erosion process, nanoparticles that are oxidation resistant to air exposure at a temperature higher than 650° C.;
forming a nanoparticle-dispersed solution including the nanoparticles contained within a solvent fluid including a dielectric material;
depositing the nanoparticle-dispersed solution onto a surface of a light absorbing material; and
drying or curing the nanoparticle-dispersed solution to form a coating having a particular spectral absorptivity and spectral emissivity, the coating formed of a composite material including the nanoparticles embedded in the dielectric material.
2. The method as in claim 1 , further comprising producing the nanoparticles by one or more of chemical synthesis, mechanical pulverization, or atomization.
3. The method as in claim 1 , wherein the depositing includes implementing at least one of spin coating, drop casting, spray coating, or inkjet printing.
4. The method as in claim 1 , wherein the solvent fluid includes at least one of water, an organic fluid, a glass precursor, or a sol-gel precursor.
5. The method as in claim 1 , wherein the nanoparticles include a semiconductor material including at least one of silicon (Si), germanium (Ge), SiGe, silicon boride, PbTe, PbSe, PbS, or metal silicides.
6. The method as in claim 1 , wherein the nanoparticles include a metallic material including at least one of tungsten (W), chromium (Cr), nickel (Ni), or molybdenum (Mo).
7. The method as in claim 1 , wherein the light absorbing material includes a metallic substrate and is capable of reflecting infrared radiation.
8. The method as in claim 1 , further comprising:
forming pillar structures in the coating,
wherein the coating is structured to include a base layer formed of the composite material and attached to the surface of the light absorbing material, and a surface layer over the base layer having the pillar structures extending outward.
9. The method as in claim 1 , wherein the light absorbing material includes a surface of a solar thermal energy collector device.
10. The method as in claim 1 , further comprising, prior to forming the nanoparticle-dispersed solution, forming a protective coating over the nanoparticles, the protective coating providing resistance to oxidation of the nanoparticles.
11. The method as in claim 10 , wherein the protective coating includes silicon boride.
12. The method as in claim 10 , wherein the forming the protective coating includes performing at least one of chemical vapor deposition (CVD), combustion synthesis deposition, physical vapor deposition (PVD), electroless plating, chemical functionalization of the external surface of the nanoparticles, or heat-assisted diffusion by mixing of the nanoparticles and the protective coating material or a precursor of the protective coating material.