High-efficiency, metamorphic multijunction cells have been fabricated by growing GaInP/GaInAs subcells that are lattice-mismatched to an active Ge substrate, resulting in GaInP/GaInAs/Ge 3-junction (3J) cells. The efficiency dependence of this 3J cell on lattice-constant of the top two cells and on sub-lattice ordering in the GaInP top cell is presented. A variety of composition-graded buffers have been explored through X-ray diffraction reciprocal space mapping to measure strain in the cell layers, and transmission electron microscopy to minimize misfit and threading dislocations. Quantum efficiency is measured for metamorphic 1.3-eV Ga0.92In0.08As (8%-In GalnAs) cells and 1.75-eV Ga0.43In0.57P cells grown on a Ge substrate, as well as for the 3J cell based on 4%-In GalnAs. Three-junction Ga0.43In0.57P/Ga0.92In0.08As/Ge cells with 0.50% lattice-mismatch to the Ge substrate are measured to have AM0 efficiency of 27.3% (0.1353 W/cm2, 28°C), similar to high-efficiency, conventional GaInP/GaAs/Ge 3-junction cells based on the GaAs lattice constant.