Patent ID: 8753918

Claim:
A method of forming a solar cell comprising: providing a semiconductor body including at least one photoactive junction; forming a semiconductor contact layer composed of GaAs deposited over the semiconductor body; depositing a metal contact layer including a germanium layer and a palladium layer over the semiconductor contact layer; and sintering the metal contact layer so that the specific contact resistance is less than 5×10 −4 ohms-cm 2 , wherein the semiconductor body includes an upper first solar subcell, a middle second solar subcell, a graded interlayer, and a lower third solar subcell, wherein the upper first solar subcell has a first band gap; wherein the middle second solar subcell has a second band gap smaller than said first band gap; wherein the graded interlayer disposed over said middle second solar subcell is compositionally graded to lattice match the middle second solar subcell on one side and the lower third solar subcell on the other side; and wherein the lower third solar subcell is disposed over said graded interlayer and has a fourth band gap smaller than said second band gap such that said lower third solar subcell is lattice mismatched with respect to said middle second solar subcell.