Abstract: Multijunction solar cells that may include a first solar subcell with a first band gap, and a second solar subcell disposed over the first solar subcell and having a second band gap smaller than said first band gap. The solar cells may also include a grading interlayer disposed over the second solar subcell that may include a third band gap greater than the second band gap. The grading interlayer may not include phosphorus. The solar cells may also include a third solar subcell disposed over the interlayer that is lattice mismatched with respect to the second solar subcell. The third solar subcell may have a fourth band gap smaller than the third band gap.