Development of Front Surface, Spectral Control Filters with Greater Temperature Stability for Thermophotovoltaic Energy Conversion

Spectral control is an important consideration in achieving high conversion efficiency with thermophotovoltaic (TPV) energy conversion systems. TPV modules using front surface filters as the primary spectral control device have demonstrated conversion efficiencies in excess of 20% with power densities in excess of 0.4 W/cm{sup 2}. The front surface filter we are developing is a short pass, long wavelength reflection filter consisting of an interference filter deposited on a plasma filter. The materials used in the interference filter must exhibit high broad band transmission and good film quality and sufficient temperature stability at the operating temperature of the TPV cells and over any potential temperature excursions that may occur. Three high refractive index materials that offer good potential for use in TPV spectral control filters are antimony selenide (Sb{sub 2}Se{sub 3}), antimony sulfide (Sb{sub 2}S{sub 3}), and gallium telluride (GaTe). The highest spectral efficiency has been demonstrated using Sb{sub 2}Se{sub 3}; however this material develops significant near infrared (NIR, 0.72-2.5 {micro}m) absorption at temperatures in excess of 90 C. The other two materials are being developed as high temperature alternatives to Sb{sub 2}Se{sub 3}. TPV filters using GaTe and Sb{sub 2}S{sub 3} have been designed and fabricated, and initial results indicate that GaTe based filters are capable of operation at temperatures of 150 C or greater. Measured performance of TPV filters containing Sb{sub 2}Se{sub 3}, GaTe and Sb{sub 2}S{sub 3} are presented, along with the impact that these have on TPV module performance