Infrared materials for thermophotovoltaic applications

Thermophotovoltaic generation of electricity is attracting renewed attention due to recent advances in low bandgap (0.5-0.7 eV) III-V semiconductors. The use of these devices in a number of applications has been reviewed in a number of publications.(1-4) Two potential low-bandgap diode materials are InxGa1-xAsySb1-y and InxGa1-xAs. The performance of these devices are comparable, (quantum efficiency, open circuit voltage, fill factor) despite the latter's long-term development for optoelectronics. For an 1100 degrees C blackbody, nominally 0.55 eV devices at 25 degrees C exhibit average photon-weighted internal quantum efficiencies of 70-80%, open circuit voltage factors of 60-65%, and fill factors of 65-70%. Equally important as the energy conversion device is the spectral control filter that effectively transmits above bandgap radiation into the diode and reflects the below bandgap radiation back to the radiator. Recent developments in spectral control technology, including InGaAs plasma filters and nonabsorbing interference filters are presented. Current tandem filters exhibit spectral utilization factors of similar to 65% for an 1100 degrees C blackbody.