Patent ID: 8536445

Claim:
A method of forming a multijunction solar cell comprising an upper subcell, a middle subcell, and a lower subcell, the method comprising: providing a first substrate composed of GaAs or Ge for the epitaxial growth of semiconductor material; growing a first solar subcell composed of InGa(Al)P on said first substrate having a first band gap; growing a second solar subcell composed of In 0.015 GaAs over said first subcell having a second band gap smaller than said first band gap; and growing a grading interlayer over said second solar subcell, said interlayer composed of InGaAlAs and having a third band gap greater than said second band gap, the band gap of the InGaAlAs grading interlayer being constant; and growing a third solar subcell composed of In 0.30 GaAs over said grading interlayer having a fourth band gap smaller than said second band gap such that said third solar subcell is lattice mismatched with respect to said second solar subcell, wherein the grading interlayer achieves a transition in lattice constant from the second subcell to the third subcell.