Highly-Efficient Near-Field ThermoPhotoVoltaics Using Surface-Polariton Emitters and Thin-Film Photo Voltaic-Cell Absorbers

A near-field ThermoPhotoVoltaic system comprises a hot emitter and a cold absorbing PhotoVoltaic cell separated by a small gap. The emitter emits hot photons and includes a polaritonic material that supports a surface-polaritonic mode. The PhotoVoltaic cell has a metallic back electrode and includes a semiconductor that absorbs the photons and supports guided photonic modes. The surface-polaritonic mode and the first guided photonic mode resonantly couple at a frequency slightly above the semiconductor bandgap. The system material and geometrical parameters are such that the surface-polaritonic mode and the first guided photonic mode are approximately impedance-matched, so that power is transmitted at frequencies just above the semiconductor bandgap, even for relatively large gap widths, while the power transmitted at other frequencies is relatively small, leading to high system efficiency. Also described the PhotoVoltaic cell's front electrode, which may include highly-doped semiconductor regions, thin conducting oxide or silver films, or graphene layers.