NOVELTY - The multijunction solar cell comprises a substrate (301), a first solar subcell disposed over the substrate and having a first band gap, a second solar subcell disposed over the first solar subcell having a second band gap greater than the first band gap and lattice matched to the first solar subcell, a third solar subcell disposed over the second solar subcell having a third band gap greater than the second band gap and lattice matched with respect to the second subcell, and a germanium silicon tin buffer layer (303) deposited over the substrate.    USE - The multijunction solar cell is useful in satellite and other space related applications.    ADVANTAGE - The multijunction solar cell has light weight, high power and energy conversion efficiency, reduced interface recombination loss, improved photogenerated current densities and high environmental protection.    DETAILED DESCRIPTION - The multijunction solar cell comprises a substrate (301), a first solar subcell disposed over the substrate and having a first band gap, a second solar subcell disposed over the first solar subcell having a second band gap greater than the first band gap and lattice matched to the first solar subcell, a third solar subcell disposed over the second solar subcell having a third band gap greater than the second band gap and lattice matched with respect to the second subcell, a germanium silicon tin buffer layer (303) deposited over the substrate, a germanium silicon tin back surface field layer (304) deposited over the buffer layer, a germanium silicon tin window layer deposited over the first solar subcell, and a tunnel diode disposed over the first solar subcell. The first solar subcell has a band gap of 0.9 eV. The second solar subcell has a band gap of 1.35 eV. The third solar subcell has a band gap of 1.75 eV. The solar cell further comprises a bottom solar subcell composed of germanium silicon tin having a first band gap of 0.7-1.2 eV, middle solar subcells disposed over the bottom solar subcell each having a band gap of 1-2.4 eV, greater than the first band gap and lattice matched to the bottom solar subcell, and a top solar subcell disposed over the middle solar subcells and having a third band gap of 1.6-2.4 eV, which is greater than the band gap the uppermost middle solar subcell and lattice matched with respect to the middle subcells.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the solar cell.    Substrate (301)    Nucleation layer (302)    Buffer layer (303)    Back surface field layer (304)    P-base layer. (305)