Inverted metamorphic multijunction solar cell including a metamorphic layer

A method of manufacturing a solar cell, the method comprising:

• providing a first substrate;
• forming, on the first substrate, a first solar subcell having a first band gap;
• forming a second solar subcell adjacent to the first solar subcell and having a second band gap smaller than the first band gap of the first solar subcell;
• forming a third solar subcell adjacent to the second solar subcell and having a third band gap smaller than the second band gap of the second solar subcell;
• forming a graded interlayer adjacent to the third solar subcell, the graded interlayer having a fourth band gap that is greater than the third band gap of the third solar subcell, wherein the graded interlayer is composed of a compositionally step-graded series of (InxGa1-x)yAl1-yAs layers with monotonically changing lattice constant, with x and y having respective values such that the band gap of the graded interlayer remains constant throughout its thickness, and wherein 0<x<1 and 0<y<1;
• forming a fourth solar subcell adjacent to the graded interlayer, the fourth solar subcell having a fifth band gap smaller than the third band gap of the third solar subcell wherein the fourth solar subcell is lattice mismatched with respect to the third solar subcell, and wherein the graded interlayer provides a transition in lattice constant from the third solar subcell to the fourth solar subcell;
• forming a fifth solar subcell adjacent to the fourth solar subcell and having a sixth band gap smaller than the fifth band gap of the fourth solar subcell;
• mounting a surrogate substrate over the fifth solar subcell;
• and
• subsequently removing the first substrate.