A method of forming a multijunction
solar cell comprising at least an upper subcell, a middle subcell, and a lower subcell, the method including forming a first alpha layer over said middle solar subcell using a surfactant and
dopant including
selenium, the first alpha layer configured to prevent
threading dislocations from propagating; forming a metamorphic grading interlayer over and directly adjacent to said first alpha layer; forming a second alpha layer using a surfactant and
dopant including
selenium over and directly adjacent to said grading interlayer to prevent
threading dislocations from propagating; and forming a lower solar subcell over said grading interlayer such that said lower solar subcell is lattice mismatched with respect to said middle solar subcell.