Metal Silicide Matched Emitters for Use in Thermophotovoltaic Generators

This contract addressed the issue of the spectral selectivity of emitters in thermophotovoltaic electric generators. In these systems, a fuel is burned to heat an emitter, which radiates energy to photovoltaic cells. One critical factor in overall system efficiency and output power is the percentage of radiant energy within the band of the photovoltaic cells. This contract investigated various emitter coatings in order to maximize radiant energy within the band of the photovoltaic cells being used, while minimizing the out-of-band energy. An appropriate coating sequence has been identified and successfully tested. The goal was to tune the spectrum for gallium antimonides photovoltaic cells, because these cells respond to longer wavelengths than traditional photovoltaic cells, and because these cells are practical to manufacture. Of the refractory metals investigated, tungsten proved to be the most stable. With an anti-reflective coating over the tungsten, the spectrum can be finely tuned for the 1.8 micron band-edge of gallium antimonides cells.