Four junction metamorphic multijunction solar cells for space applications

A method of fabricating a four junction solar cell for deployment in space in AM0 spectra in a specific earth orbit characterized by a predetermined temperature and radiation environment comprising:

• providing a defined predetermined time and defined temperature in the range of 40° to 100° Centigrade after initial deployment, such time being at least one year and in the range of one to twenty-five years;
• determining the amount of radiation experienced by the solar cell after deployment at the predetermined time in the specific earth orbit after deployment;
• simulating the effect of such radiation and temperature on a plurality of upper first, second and third solar subcell candidates for implementation by a computer program;
• and
• identifying the composition and band gaps of the upper first, second and third subcells that maximizes the efficiency of the solar cell at that predetermined time so that the selection of the composition of the subcells and their band gaps maximizes the efficiency at high temperature (in the range of 50 to 100 degrees Centigrade) in deployment in space at a specific predetermined time after initial deployment (referred to as the beginning of life or BOL), such predetermined time being referred to as the end-of-life (EOL), and being at least five years after the BOL, such selection being designed not to maximize the efficiency at BOL but to increase the solar cell efficiency at the EOL while disregarding the solar cell efficiency achieved at the BOL, such that the solar cell efficiency designed at the BOL is less than the solar cell efficiency at the BOL that would be achieved if the selection were designed to maximize the solar cell efficiency at the BOL.

A method of manufacturing a multijunction solar cell comprising:

• providing a germanium growth substrate;
• forming a first solar subcell over or in the growth substrate;
• growing a graded interlayer over the growth substrate;
• growing a first middle solar subcell over und lattice mismatched with respect to the growth substrate and having a band gap in the range of 1.2 to 1.35 eV;
• growing a second middle solar subcell over the first middle subcell and having a band gap in the range of approximately 1.61 to 1.8 eV;
• and
• growing an upper subcell disposed over the last middle subcell and having a band gap in the range of 1.95 to 2.20 eV;
• wherein the graded interlayer is compositionally graded to lattice match the growth substrate on one side and the first middle solar subcell on the other side, and is composed of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter throughout its thickness being greater than or equal to that of the growth substrate;
• and
• wherein the selection of the composition of the subcells and their band gaps maximizes the efficiency at high temperature (in the range of 50 to 100 degrees Centigrade) in deployment in space at a specific predetermined time after initial deployment (referred to as the beginning of life or BOL), such predetermined time being referred to as the end-of-life (EOL), and being at least five years after the BOL, such selection being designed not to maximize the efficiency at BOL but to increase the solar cell efficiency at the EOL while disregarding the solar cell efficiency achieved at the BOL, such that the solar cell efficiency designed at the BOL is less than the solar cell efficiency at the BOL that would be achieved if the selection were designed to maximize the solar cell efficiency at the BOL.