One-dimensional and two-dimensional photonic crystals are used to modify the emitter spectrum and achieve higher efficiency. Samples of one-dimensional and two-dimensional photonic crystals are produced in the Integrated Circuits Laboratory and the Nanostructures Laboratory.

Theory:

A fuel, e.g. gasoline, is used to heat an emitting surface to approximately 1500K, and the emitter in turn radiates high-energy photons. The PV cells on which this spectrum is incident converts the photons with energies higher than the bandgap of the PV cell into electricity. The remaining portion of the spectrum which cannot be converted is dissipated as heat in the PV cell.

Using a GaSb PV cell, with a bandgap energy of 0.7eV, (1.7µm in wavelength) requires a filter which passes photons whose wavelengths are shorter than 1.7 µm to the PV cell while reflecting the remaining photons back to the emitter.