Methods of fabricating photovoltaic devices include forming a plurality of subcells in a vertically stacked arrangement on a semiconductor material, each of the subcells being formed at a different temperature than an adjacent subcell such that the adjacent subcells have differing effective band-gaps. The methods of fabricating also include inverting the structure, attaching another substrate to a second semiconductor material, and removing the substrate. For example, each of the subcells may comprise a III-nitride material, and each subsequent subcell may include an indium content different than the adjacent subcell. Novel structures may be formed using such methods.