A photovoltaic apparatus includes a p-layer having a bandgap greater than about 2 eV, an n-layer having a bandgap greater than about 2 eV, and an absorber layer between the p-layer and the n-layer, wherein the absorber layer includes SiGe. The ratio of Si to Ge in the absorber layer can be selected to obtain an absorber bandgap between about 1.1 and about 1.4 eV.