Integrated bandpass filter contacts for radioisotope thermophotovoltaic cells

Abstract

Smaller spacecraft deployed on deep space missions will require improved electrical power generation efficiency above that which is presently available from radioisotope powered thermoelectric devices. Low bandgap thermophotovoltaic (TPV) devices, when used in conjunction with spectrally modified or filtered emitters, offer the promise of 4 to 5 times efficiency improvement. Integrating spectral filters into PV cell contacts can further improve the efficiency of TPV systems. An inductively resonant mesh metal film filter deposited directly on the surface of the TPV cell can serve as both a bandpass filter to modify the emitted radiant energy spectrum and as a shadowless, low-resistivity electrical contact to the cell. By significantly reducing traditional grid shadow losses, junction sheet resistance losses, and grid series resistance losses, the overall TPV system efficiency can be improved by 10% to 16% depending on the TPV cell operating current density and design geometry. These innovative contacts become even more beneficial in Earth based applications where very high operating current densities are required by economics. With the availability of these low-loss TPV devices at appropriate unit costs, they can find uses in such commercial TPV technologies as selfpowered gas fumaces and water heaters, and Earth-based solar concentrator TPV systems.

The challenge of high-performance selective emitters for thermophotovoltaic applications

“…Electron beam lithography and masked ion beam lithography techniques have been employed to fabricate optical filters to be used in TPV systems designed to reach a heat-to-electricity conversion efficiency of 25% [34]. EDTEK Inc. patented TPV filters based on a highdensity array of slotted antenna elements etched into a thin gold film [35]. Each cross-shaped mesh element has typical dimensions of 80 × 450 nm 2 .…”