A silicon microcavity selective emitter with smooth surfaces for thermophotovoltaic power generation

Metal-coated silicon microcavities have been developed as a selective emitter for high-efficiency thermophotovoltaic power generation. In order to examine the effect of surface roughness, two different metal deposition methods, electron-beam evaporation and vacuum arc evaporation, are employed. The surface roughness of a thin metal film with vacuum arc evaporation is much less than that with electron-beam evaporation. For 1.8 µm microcavities with a 50 nm thick Ti film, an emittance peak appears at the wavelength of 3.2 µm, which corresponds well to the first electromagnetic resonance mode. Microcavities with vacuum-arc-evaporated metal exhibit clear electromagnetic resonance modes in the shorter wavelength region, while the emittance reduces to the value for smooth surfaces in the longer wavelength region. By using a Ge photovoltaic cell, the energy conversion efficiency with the present microcavity at 915 °C is found to be 3.2%, which is in good agreement with the estimates with an equivalent circuit model. Assuming the radiation view factor of 0.94, the energy conversion efficiency based on the present model is increased to 7.4% for the emitter temperature of 1200 °C