Thermophotovoltaic spectral control

Abstract

Spectral control is a key technology for thermophotovoltaic (TPV) direct energy conversion systems because only a fraction (typically less than 25%) of the incident thermal radiation has energy exceeding the TPV cell bandgap energy, Eg, and can thus be converted to electricity. The goal for TPV spectral control in most applications is twofold: 1) Maximize TPV efficiency by minimizing transfer of low energy, below bandgap photons from the radiator to the TPV cell and 2) Maximize TPV surface power density by maximizing transfer of high energy, above bandgap photons from the radiator to the TPV cell. TPV spectral control options include: front surface filters (e.g. interference filters, plasma filters, interference/plasma tandem filters, and frequency selective surfaces), back surface reflectors, and wavelength selective radiators. System analysis shows that spectral performance dominates TPV cell performance in any practical TPV system, and that low bandgap TPV cells enable both higher efficiency and power density when spectral control limitations are considered. Lockheed Martin has focused its efforts on front surface tandem filters which have achieved spectral efficiencies of ∼83% for Eg = 0.52 eV and ∼76% for Eg = 0.60 eV for a 950°C radiator temperature. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc.