INFRARED MATERIALS FOR THERMOPHOTOVOLTAIC APPLICATIONS

Thermophotovoltaic generation of electricity is attracting renewed att ention due to recent advances in low bandgap (0.5-0.7 eV) III-V semico nductors. The use of these devices in a number of applications has bee n 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 vol tage, fill factor) despite the latter's long-term development for opto electronics. For an 1100 degrees C blackbody, nominally 0.55 eV device s at 25 degrees C exhibit average photon-weighted internal quantum eff iciencies of 70-80%, open circuit voltage factors of 60-65%, and fill factors of 65-70%. Equally important as the energy conversion device i s the spectral control filter that effectively transmits above bandgap radiation into the diode and reflects the below bandgap radiation bac k 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 fa ctors of similar to 65% for an 1100 degrees C blackbody.