Inverted metamorphic multijunction solar cells for space applications

A multijunction solar cell comprising:

• an upper first solar subcell having a first band gap;
• a second solar subcell adjacent to said first solar subcell and having a second band gap;
• a third solar subcell adjacent to said second solar subcell and having a third band gap;
• a graded interlayer adjacent to said third solar subcell, said graded interlayer having a fourth band gap greater that said third band gap;
• and
• a fourth solar subcell adjacent to said graded interlayer, said fourth subcell having a fifth band gap such that said fourth subcell is lattice mismatched with respect to said third solar subcell;
• wherein the graded interlayer is compositionally graded to lattice match the third solar subcell on one side, and the lower fourth solar subcell on the other side, and is composed of (InxGa1-x)yAl1-y As with 0 < x < 1, 0 < y <1, with x and y selected such that the band gap of the graded interlayer remains at a constant value throughout its thickness and is composed of four to fifteen distinct adjacent layers, the first layer of the graded interlayer having an amount of indium in the range of 4 to 12% per mole fraction greater than the amount of indium in the adjacent layer on which it is grown, and the second and subsequent layers of the graded interlayer having an amount of indium in the range of 2 to 6% greater than the adjacent region in which it is grown, wherein the thickness of the first layer of the graded interlayer is at least twice the thickness of each of the second and subsequent layers of the graded interlayer.

A method of manufacturing a solar cell comprising:

• providing a first substrate;
• depositing on the first substrate a first sequence of layers of semiconductor material forming a first solar subcell, a second solar subcell, and a third solar subcell;
• depositing on said third solar subcell a first grading interlayer;
• depositing on said first grading interlayer a second sequence of layers of semiconductor material forming a fourth solar subcell, the fourth solar subcell being lattice mismatched to the third solar subcell;
• depositing on said fourth solar subcell a second grading interlayer;
• depositing on said second grading interlayer a third sequence of layers of semiconductor material forming a fifth solar subcell, the fifth solar subcell being lattice mismatched to the third solar subcell;
• mounting and bonding a surrogate substrate on top of the sequence of layers;
• and removing the first substrate;
• wherein the first graded interlayer is compositionally graded to lattice match the third solar subcell on one side and the lower fourth solar subcell on the other side, and is composed of (InxGa1-x)yAl1-yAs with 0 < x < 1, 0 < y < 1, and x and y selected such that the band gap remains in the range of 1.42 to 1.60 eV throughout its thickness and is composed of at least four distinct adjacent regions, the first region layer having an amount of indium in the range of 4 to 12% per mole fraction greater than the amount of indium in the adjacent layer on which it is grown, and the second and subsequent regions layers having an amount of indium in the range of 2 to 6% greater than the adjacent region in which it is grown;
• and
• wherein the second graded interlayer is compositionally graded to lattice match the fourth solar subcell on one side and the lower fifth solar subcell on the other side, and is composed of (InxGa1-x)yAl1-yAs with 0 < x < 1, 0 < y < 1, and x and y selected such that the band gap remains in the range of 1.2 eV to 1.6 eV throughout its thickness.