Investigations of metamorphic (Al)GaInP for III?V multijunction photovoltaics

We explore the lattice constant and Al content parameter space supporting (Al)GaInP materials with direct bandgaps >2.0 eV, to assess such materials for applications to future ≥4 junction multijunction photovoltaics. (Al_zGa_1-z)_xIn_1-xP test structures and prototype solar cells were grown by molecular beam epitaxy lattice-matched to either GaAs_yP_1-y virtual substrates or GaAs substrates over a range of Al contents and lattice constants. We observe significant anneal-induced improvements in material quality and solar cell performance in all compositions considered. Comparing test structures and solar cells with ~2.0 to ~2.1 eV bandgaps suggests that (Al)GaInP compositions with tensile-misfit (vs. GaAs) show potential to outperform lattice-matched (Al)GaInP compositions with higher Al fractions in future multijunction cells requiring top cell bandgaps >2.0 eV.