The development of Ge bottom cell for monolithic and stacked multi-junction applications

Ge solar cells have applications in space solar systems as well as terrestrial concentrator systems. Progress in fabrication of Ge cells to work under GaAs is described. While the fabrication of monolithic GaAs/Ge cells has not led to the theoretically predicted efficiencies, the Ge bottom cell still has applications in the monolithic stack. Currents achieved in Ge are sufficient for it to serve as a bottom cell of the three-junction GaAs/Ge stack. The diffusion length measured in Ge cells is sufficient to fabricate good cells. The effect of a BSR on electrical performance is considered. Radiation performance results for Ge cells are reported