Optimization of low cost germanium receiver cells for thermophotovoltaic applications

When thermophotovoltaic (TPV) systems are compared to classical PV systems, two main aspects are distinctly important. First, due to the small distance between the receiver cells and heat source, a high photon flux will be incident on the cell. Secondly, due to the relatively low temperature of the heat source compared to the sun, the emitted photons will have a high wavelength. These two differences result in a need to apply optical confinement in the receiver cells, as well as an optimized front contact structure. In this paper, the results on the realization of optical confinement together with the application of local contacting on the rear with laser fired contacts (LFC) will be discussed. A germanium TPV cell having a LFC rear contact showed an efficiency of 6.3% when illuminated with the AM1.5G spectrum. Results on optimizing the front contact structure will be given where the quality of these contacts has been tested under concentrated illumination (AM1.5G × 1–70). In these experiments we have shown that the realized front contact, consisting of a stack of Pd/Ag, performs well up to concentration ratio´s of 70 suns which proves that this type of contact is suitable for application in TPV systems.