Patent ID: 7960201

Claim:
A method of forming a multijunction solar cell comprising an upper subcell, a middle subcell, and a lower subcell comprising: providing a first substrate for the epitaxial growth of semiconductor material; forming an upper first solar subcell on said first substrate having a first band gap; forming a middle second solar subcell over said upper first solar subcell having a second band gap smaller than said first band gap; forming a graded interlayer over said middle second solar subcell; forming a lower third solar subcell over said graded interlayer having 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; forming a metal contact layer over said lower third solar subcell; attaching a surrogate second substrate over said metal contact layer and removing said first substrate; and etching a first trough around the periphery of said multijunction solar cell through the solar subcells and said graded interlayer to the metal contact layer so as to form a mesa structure on said surrogate second substrate to form a plurality of contact pads on said metal contact layer, said plurality of contact pads spaced apart along said metal contact layer by intermediate sections, said contact pads having a larger surface area than an adjacent one of said intermediate sections.