Multijunction metamorphic solar cells

A multijunction solar cell comprising:

• a growth substrate;
• a first solar subcell disposed over or in the growth substrate;
• a tunnel diode disposed over the first solar subcell;
• a grading interlayer directly disposed over the tunnel diode;
• a sequence of layers of semiconductor material forming a solar cell disposed over the grading interlayer comprising a plurality of subcells including a second solar subcell disposed over and lattice mismatched with respect to the growth substrate, and at least a third solar subcell composed of a semiconductor compound including at least indium, gallium, arsenic and phosphorus and disposed over the second solar subcell;
• wherein the grading interlayer has a band gap equal to or greater than that of the second subcell and is compositionally graded to lattice match the growth substrate on one side and the second subcell on the other side;
• and being composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter in each of the sublayers of the grading interlayer throughout its thickness being greater than or equal to the lattice constant of the growth substrate;
• and
• a fourth or upper solar subcell disposed over the third solar subcell compound of a semiconductor compound including at least aluminum, indium, and having a band gap in the range of 1.95 eV to 2.20 eV, wherein either the third solar subcell or the fourth solar subcell, or both has an aluminum content in excess of 17.5% by mole fraction,

A multijunction solar cell comprising:

• a growth substrate;
• a first solar subcell disposed over or in the growth substrate;
• a grading interlayer directly disposed over the growth substrate;
• a sequence of layers of semiconductor material forming a solar cell disposed over the grading interlayer comprising a plurality of subcells including:
• a second solar subcell directly disposed over and lattice mismatched with respect to the growth substrate, and
• a third solar subcell disposed over and lattice matched with the second solar subcell;
• and an upper solar subcell disposed over and lattice matched to the third solar subcell;
• wherein the grading interlayer has a band gap equal to or greater than that of the second subcell and is compositionally graded to lattice match the growth substrate on one side and the second subcell on the other side;
• and being composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice constant in each of the sublayers throughout its thickness being greater than or equal to the lattice constant of the growth substrate, and includes N step-graded sublayers where N is an integer and 1≤N≤10, wherein each successive sublayer has an incrementally greater lattice constant than the sublayer below it and grown in such a manner that the graded sublayer is fully relaxed (i.e., not in tension or compression);
• wherein either the upper solar subcell or the third solar subcell has an aluminum content in excess of 17.5% by mole fraction.

A method of manufacturing a multijunction solar cell for use in a space vehicle 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, followed by a sequence of layers of semiconductor material using a deposition process to form a solar cell comprising a plurality of subcells including:
• a second solar subcell disposed over and lattice mismatched with respect to the growth substrate and having a band gap in the range of 1.0 eV to 1.41 eV;
• a third solar subcell disposed over the second subcell and having a band gap in the range of approximately 1.35 eV to 1 73 eV;
• a fourth or upper subcell disposed over the third solar subcell and a band gap in the range of 1.95 eV to 2.20 eV;
• wherein the graded interlayer is compositionally graded to lattice match the growth substrate on one side and the second 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 either the third solar subcell or the fourth solar subcell, or both, has an aluminum content in excess of 17.5% by mole fraction.