Spectral control development for thermophotovoltaics
Gallium Antimonide (GaSb) infrared photovoltaic cells are light weight whereas batteries are heavy. The specific energy in a hydrocarbon fuel is high at 12,900 W-hr per kg but a lithium ion rechargeable battery has a specific energy of only 145 W-hr per kg. A 10% efficient portable lightweight thermophotovoltaic (TPV) cylindrical generator when compared with a battery can have 6.5 times higher specific energy, operates 7 times longer, and be quickly refueled. The key is the 10% efficiency goal. This efficiency goal depends on matching the spectrum from a combustion heated ceramic IR emitter to the response band of the IR PV cell. Herein, spectral measurements are presented for a propane burner and ceramic IR emitter assembly surrounded by a fused silica glass envelope. The cylindrical IR ceramic emitter consists of an array of NiO doped MgO rods or slats. The Ni ion emission line is centered at 1.6 microns and it matches the GaSb IR response band extending out to 1.8 microns. The ceramic IR emitter is combustion heated to approximately 1200 C. The fuel and air combustion efficiency and hot gas coupling efficiency to the IR emitter are also important parameters.
Gallium Antimonide Thermophotovoltaic: Simulation and Electrical Characterization Under Different Spectral Filtration Wavelengths
Gallium Antimonide (GaSb) Thermophotovoltaic (TPV) cell is a well-known device for waste-heat harvesting technology. To date, the conversion efficiency of the GaSb TPV cell remains low due to the presence of electrical and spectral losses. In this study, a GaSb TPV cell model is developed using the Silvaco TCAD simulation software. Validation on the simulation model was performed under atmospheric (AM) 1.5 standard test condition (STC) and TPV illumination conditions. Through the validation processes, a set of GaSb physical parameters that are reliable to be used for GaSb TPV cell simulation was established. Under AM1.5 testing condition, the electrical characteristic and performance of GaSb TPV of the reference cell were obtained from an experimental characterization on commercialized devices. A deviation in fill factor and cell efficiency was found between the cell sample and simulation model under AM1.5 illumination. This is due to the presence of resistance losses in the device. Nevertheless, a percentage error of below 3% was achieved under 1200 ° C TPV spectrum. Besides, it was found that a spectral filter that cuts at 2 μm increases the cell efficiency from 11.51% to 19.10% with a power output of 1.33 W/cm2. The finding in this study demonstrates the importance of minimizing the electrical losses and the determination of an optimal filtered spectrum wavelength for developing highperformance GaSb TPV cell.
TPV History from 1990 to Present & Future Trends
Herein, the history of TPV at JX Crystals over the last 15 years is described. Our focus has been on commercial application for TPV components and systems. JX Crystals began as a spin off company when the inventors of the GaSb cell left Boeing with a license to make that cell at JX Crystals. We recognized that III‐V IR sensitive cells such as the GaSb cell were enabling for TPV systems. We began pilot production of GaSb cells in 1994. However, while these cells are necessary for TPV, they are not sufficient by themselves and the development of other system components has been necessary. The development of spectral control and burner and recuperator subsystems will be described here. Unfortunately, a complete TPV system still needs to be fully developed. Various R&D efforts around the world are underway targeting this objective. JX Crystals continues to supply small quantities of cells for these development efforts. Given such a TPV system, cell prices can fall dramatically with volume production.