Description: A thermophotovoltaic (TPV) system is a promising energy conversion device that generates the electric power from short wave infrared (SWIR) thermal radiation. However, it's low power throughput and poor conversion efficiency restricts the usage in practical applications. One solution for resolving these issues is to utilize a metamaterial emitter whose thermal emission band is spectrally matched to the energy conversion band of the TPV cell. However, typical frequency selective emitters (SE) emit only in a narrow frequency band, limiting the total power throughput of the TPV system. This proposal thus aims to experimentally investigate wideband metamaterial emitters, whose emission band is spectrally matched and utilizes the entire energy conversion band of the TPV cell. The innovative aspects of the proposed research are (1) to develop robust electromagnetic numerical simulation capabilities that incorporate experimentally measured material properties as a function of frequency, and device operation temperature into the design of the metamaterial emitter; (2) incorporate novel metal-nitride materials into the metamaterial structure, enabling optical property tunability through stoichiometric control, and wideband, spectrally matched thermal emission; (3) to fabricate and characterize a metamaterial emitter whose thermal emission band is spectrally matched to the energy conversion band of the target TPV cell. By improving not only the overall efficiency of TPV converters, but importantly the total power throughput, this technology will enable more efficient, compact electrical energy sources for a range of applications, which include power sources for rural and remote locations, solar power generation, waste heat recovery, and power sources for deep space exploration.

Benefits: Radioisotope Power Systems (RPS) are the preferred technology for NASA deep space missions. The proposed technology offers significant improvement in both efficiency and mass specific power performance enabling for a variety of future NASA mission concepts. The technological gains in spectral efficiency will enable the metamaterial (MM)- TPV systems to be commercialized for future NASA deep space missions.

The technological gains in efficiency and power throughput as a result of this proposed research will enable the metamaterial (MM)-TPV systems to be commercialized in a wide range of applications, including concentrated solar power generation, and portable lightweight solid-state electrical power generators. A TPV-based generator will be competitive with ICE-based power generators in terms of overall fuel efficiency. The technical discussion in this proposal details why a metamaterial selective emitter will offer sufficient overall efficiency gain to enable TPV systems to be competitive with internal combustion engine generators. Other attending performance advantages – quiet operation, no moving parts/low maintenance, ease of operation, size and weight - will enable TPV-based systems to penetrate the market.