The proposed innovation is the development of a technology that will enable the manufacture of high-efficiency (>40%), quadruple(4) junction solar cells on lightweight Ge substrates. We plan to achieve this objective by developing a new semiconductor alloy, InGaAsN, which will be employed as the 1.18 eV bottom cell in quadruple-junction [InGaP (1.8 eV) / GaInAs P(1.5 eV) / InGaAsN (1.18 eV) / Ge (0.67eV)] solar cells. The InGaAsN alloy material will be lattice matched to Ge, which is a clear improvement over existing inverted metamorphic (IMM) technology, specifically, the existing lattice-mismatched InGaAs 1.0 eV bottom cell is replaced with a lattice-matched InGaAsN 1.18 eV bottom cell. This eliminates the need to grow a thick graded buffer layer. Another advantage of this system is higher efficiency and higher reliability solar cells which can effectively be a drop in replacement to the existing Ge based space cells. At the end of this project, we expect to have developed and integrated InGaAsN - 1.18 eV material, which can be used in Ge-based multi-junction cells that have the potential to achieve efficiencies in excess of 40% at AM0, one sun illumination.