Metallic dielectric photonic crystals and methods of fabrication
A metallic-dielectric photonic crystal is formed with a periodic structure defining a plurality of resonant cavities to selectively absorb incident radiation. A metal layer is deposited on the inner surfaces of the resonant cavities and a dielectric material fills inside the resonant cavities. This photonic crystal can be used to selectively absorb broadband solar radiation and then reemit absorbed radiation in a wavelength band that matches the absorption band of a photovoltaic cell. The photonic crystal can be fabricated by patterning a sacrificial layer with a plurality of holes, into which is deposited a supporting material. Removing the rest of the sacrificial layer creates a supporting structure, on which a layer of metal is deposited to define resonant cavities. A dielectric material then fills the cavities to form the photonic crystal.
1. A system for converting solar radiation into electricity, the system comprising:
a solar concentrator to focus the solar radiation;
a wavelength selective device, in optical communication with the solar concentrator, to convert solar radiation focused by the solar concentrator over a range of incident angles from about 0° to about 70° and below a cut-off wavelength into heat energy and to reemit the heat energy as radiation in a predetermined emission band, the wavelength selective device comprising:
(i) a metallic structure defining at least one resonant cavity,
(ii) a dielectric material disposed within the at least one resonant cavity, and
(iii) an anti-reflection coating deposited on the metallic structure; and
a photovoltaic cell, in optical communication with the wavelength selective device, to convert the radiation emitted by the wavelength selective device into electricity, wherein the predetermined emission band is substantially within a band gap of the photovoltaic cell.
2. The system of claim 1 , wherein the cut-off wavelength is about 1 μm to about 5 μm.
3. The system of claim 1 , wherein metallic structure comprises:
a periodic structure defining a plurality of resonant cavities; and
a layer of metal disposed on an inner surface of at least one resonant cavity in the plurality of resonant cavities.
4. The system of claim 1 , wherein:
the metallic structure has a first thermal expansion coefficient; and
the dielectric material has a second thermal expansion coefficient less than the first thermal expansion coefficient.
5. The system of claim 1 , wherein the at least one resonant cavity supports at least one optical mode having a wavelength substantially equal to the cut-off wavelength.