A photovoltaic cell comprises a top subcell having a first band gap; a middle subcell comprising a substrate and having a second band gap, wherein the substrate comprises a first side and a second side opposite to the first side; and a bottom subcell having a third band gap, wherein the top subcell is grown on the first side of the substrate and the bottom subcell is grown on the second side of the substrate, wherein the first band gap is larger than the second band gap and the second band gap is larger than the third band gap.