This invention relates to the field of thermophotovoltaic (TPV) direct
energy conversion. In particular, TPV systems use filters to minimize
parasitic absorption of below bandgap energy. This invention constitutes
a novel combination of front surface filters to increase TPV conversion
efficiency by reflecting useless below bandgap energy while transmitting
a very high percentage of the useful above bandgap energy. In particular,
a frequency selective surface is used in combination with an interference
filter. The frequency selective surface provides high transmission of
above bandgap energy and high reflection of long wavelength below bandgap
energy. The interference filter maintains high transmission of above
bandgap energy and provides high reflection of short wavelength below
bandgap energy and a sharp transition from high transmission to high
reflection.