Multijunction solar cells on bulk GeSi substrate

A four-junction space-qualified solar cell assembly designed for operation at AMO and at a 1 MeV electron equivalent fluence of at least 1×1014 e/cm2, the solar cell comprising subcells, wherein a combination of compositions and band gaps of the subcells is designed to maximize efficiency of the solar cell at a predetermined time, after initial deployment, when the solar cell is deployed in space at AMO and at an operational temperature in the range of 40 to 70 degrees Centigrade, the predetermined time being at least five years and referred to as the end-of-life (EOL), the solar cell comprising:

• an upper first solar subcell composed of indium gallium aluminum phosphide and having a first band gap in the range of 2.0 to 2.2 eV;
• a second solar subcell adjacent to said upper first solar subcell and including an emitter layer composed of indium gallium phosphide or aluminum indium gallium arsenide, and a base layer composed of aluminum indium gallium arsenide and having a second band gap in the range of approximately 1.55 to 1.8 eV and being lattice matched with the upper first solar subcell, wherein the emitter and base layers of the second solar subcell form a photoelectric junction;
• a third solar subcell adjacent to said second solar subcell and composed of indium gallium arsenide and having a third band gap less than that of the second solar subcell and being lattice matched with the second solar subcell;
• and
• a fourth solar subcell adjacent to said third solar subcell and composed of germanium silicon and has an indirect band gap in the range of 0.7 to 1.1 eV, or 0.85 to 1.05 eV;
• wherein each of the upper first solar subcell, the second solar subcell and the third solar subcell is lattice-mismatched to the fourth solar subcell, and
• wherein a numerical sum of the band gaps of the four solar subcells, divided by four, is equal to 1.35 eV.