High Operating Temperature, Radiation-Hard MIM Thermophotovoltaic Converters

Spire Corporation proposes to investigate InGaAs thermophotovoltaic (TPV) cells optimized for high temperature operation (~150C) and radiation hardness against the 1.64MeV neutron flux likely from plutonium dioxide general purpose heat sources. We propose to develop a temperature-dependent TPV cell model and select an optimum bandgap for 150C operation with a 1100C heat spectrum, using a cell design with a thin (~1 micron vs standard ~3 micron) base that improves tolerance to diffusion length degradation from radiation. In order to increase photon absorption in this thin cell, we propose to epitaxially grow a monolithic 15 period InGaAs/InAlAs Bragg mirror to reflect about 90% of the incident usable (2 ~micron wavelength) photons back through the cell. The proposed advantage of the Bragg over a standard back metal mirror reflector is that the dielectric mirror has some ability to use strain exerted at the interfaces of the different mirror materials as a threading-to-misfit dislocation filter to further enhance the cell efficiency. We also propose to examine polyimide along with standard SiN for MIMs (monolithically integrated multijunction module) edge passivation.