Method of fabricating bifacial tandem solar cells

A method of fabricating on a semiconductor substrate bifacial tandem solar cells with subcells, the method comprising:

• growing higher bandgap subcells on one side of a substrate, the higher bandgap subcells comprising at least one periodic table group V material;
• after said growing the higher bandgap subcells, flipping the substrate;
• and
• after said flipping the substrate, growing a lower bandgap subcell on an opposite side of the substrate using non-phosphorous materials, the lower bandgap subcell comprising a bottom subcell and grading layers, the bottom subcell and the grading layers comprising at least one periodic table group V material,
• wherein the lower bandgap subcell has a lower bandgap than a substrate bandgap and the higher bandgap subcells have a higher bandgap than the substrate bandgap.