Advanced Thermophotovoltaic Cells Modeling, Optimized for Use in Radioisotope Thermoelectric Generators (RTGs) for Mars and Deep Space Missions

This is a NAVAL POSTGRADUATE SCHOOL MONTEREY CA report procured by the Pentagon and made available for public release. It has been reproduced in the best form available to the Pentagon. It is not spiral-bound, but rather assembled with Velobinding in a soft, white linen cover. The Storming Media report number is A841524. The abstract provided by the Pentagon follows: To accommodate the need for power on deep space missions, satellites must carry a source capable of providing adequate power for the life of the mission. This is currently done using radioisotope thermoelectric generators (RTGs). Current RTGs consist of a heat source, Pu-238, and a thermocouple that inefficiently converts heat into electricity. To improve the overall efficiency of RTGs, a better thermoelectric converter is needed to replace the thermocouple. This thesis examines the possible use of thermophotovoltaic (TPV) cells in RTGs. Two cells were developed and optimized for the spectrum from a 1300K blackbody that simulates the spectrum of an RTG heat source. Current TPV cells are built and tested with different thicknesses and doping levels to the most efficient design, an expensive and time-consuming method. This thesis presents a model that can predict the output of a cell under various spectra. The model can easily be changed to simulate different cell thicknesses and doping levels, and it can be changed to simulate cells of different materials. The models presented in this thesis were built using the Silvaco Virtual Wafer Fabrication software package. To prove the capabilities of this software package in designing TPV models, an initial cell was designed using a well-documented material: gallium arsenide (GaAs). Voltage-current characteristics and frequency response data were recorded from this model and compared with experimental data from a similar cell. Once the model was verified, more exotic materials could be examined: gallium antimonide (GaSb) and indium gallium arsenide (InGaAs).