A four junction solar cell and its method of manufacture including an upper first solar subcell composed of a semiconductor material having a first band gap; a second solar subcell adjacent to said first solar subcell and composed of a semiconductor material having a second band gap smaller than the first band gap and being lattice matched with the upper first solar subcell; a third solar subcell adjacent to said second solar subcell and composed of a semiconductor material having a third band gap smaller than the second band gap and being lattice matched with the second solar subcell; a graded interlayer adjacent to the third solar subcell and having a fourth band gap greater than the third band gap; and a bottom solar subcell adjacent to the graded interlayer and being lattice mismatched from the third solar subcell and having a fifth band gap smaller than the fifth band gap, wherein the selection of composition of the subcells and their band gaps maximizes the efficiency of the solar cell at a predetermined temperature value (between 28 and 70 degrees Centigrade) at a predetermined time after the initial deployment in space, (the time of the initial deployment being referred to as “beginning-of-life (BOL)”), such predetermined time being referred to as the “end-of-life (EOL)” time, and such time being at least one year.