This paper focuses on the metal–organic vapor-phase epitaxy (MOVPE) growth of 2-junction (2J) solar cells where epitaxial Ga 0.29In 0.71P top and Ga 0.77In 0.23As bottom subcells are grown lattice-mismatched on a Ge substrate. Single-junction metamorphic devices with 23%-In GaInAs are grown on 100-mm dia. (0 0 1) Ge substrates. Layers are observed to be fully relaxed by high-resolution X-ray diffraction. Threading dislocation densities of 3.1×10 6 cm −2 are measured. Single-junction devices in the 1.1-eV materials demonstrate near 100% internal quantum efficiency above the band gap and an open-circuit voltage comparable to world-record silicon photovoltaic devices. The presence and strength of CuPt B ordering is explored in controlling the band gap of the Ga 0.29In 0.71P top subcell devices between 1.647 and 1.593 eV. An order parameter of 0.28 is measured by X-ray measurement of the forbidden 1 2 ( 1 1 5 ) reflection for the low-band gap material. The presence of low-resistance shunt pathways is observed as the present obstacle to reaching the potential efficiency of 30% for these metamorphic dual-junction devices.