High Efficiency Graphene/Wide Band-Gap Semiconductor Heterojunction Solar Cells

A method to form a solar cell, comprising:

• providing a lower copper foil having a top surface and a bottom surface;
• providing a zinc foil having a top surface and a bottom surface, the bottom surface being in contact with the top surface of the copper foil throughout at least a portion of the bottom surface area of the zinc foil;
• using a hydrothermal synthesis process to form a plurality of nanowire cores on the upper surface of the zinc foil, the nanowire cores comprising zinc oxide, wherein at least a majority of the nanowire cores are substantially aligned to one another and extend generally perpendicular to the foil and being electrically connected to the foil substrate at a first end of nanowire cores, the hydrothermal synthesis process forming a substantially continuous coating of zinc oxide between the zinc oxide nanowire cores;
• treating the nanowire cores in a post-growth annealing process to reduce structural defects at the surface of the nanowires cores;
• depositing a graphene material on at least part of the nanowire cores.

A photovoltaic solar cell apparatus comprising at least one solar cell, the at least one solar cell having been prepared by a method comprising:

• providing a foil substrate;
• forming a plurality of nanowire cores on the foil substrate using a hydrothermal synthesis process, the nanowire cores comprising zinc oxide, wherein at least a majority of the nanowire cores are substantially aligned to one another and extend generally perpendicular to the foil substrate and being electrically connected to the foil substrate at a first end of nanowire cores, the hydrothermal synthesis process forming a substantially continuous coating of a nonconductive material on the foil substrate between the zinc oxide nanowire cores;
• surrounding the plurality of zinc oxide nanowire cores with graphene oxide;
• forming a plurality of nanowire core/shell structures by maintaining the zinc oxide nanowire cores and graphene oxide under conditions sufficient to thermally reduce at least some of the graphene oxide to form a plurality of shells, each shell comprising reduced graphene oxide and being conformally disposed about a portion of a respective nanowire core to form a photovoltaic junction;
• forming a first conducting electrode electrically connected to the foil substrate and providing a first electrical pathway to facilitate a movement of electrons away from the nanowire cores;
• and
• forming a second conducting electrode connected to the reduced graphene oxide shells at a second end of the nanowire core/shell structures and providing a second electrical pathway to facilitate a movement of positive charges away from the reduced graphene oxide shells.

A photovoltaic solar cell apparatus comprising:

• a foil substrate;
• a plurality of nanowire cores on the foil substrate, the nanowire cores comprising zinc oxide, wherein at least a majority of the nanowire cores are substantially aligned to one another and extend generally perpendicular to the foil substrate and electrically connected to the foil substrate at a first end of the nanowire cores;
• a substantially continuous coating of a nonconductive material on the foil substrate between the zinc oxide nanowire cores;
• a plurality of reduced graphene oxide shells, each shell comprising reduced graphene oxide, and each shell being conformally disposed about a portion of a respective nanowire core to form a plurality of nanowire core/shell structures;
• a first conducting electrode electrically connected to the foil substrate and providing a first electrical pathway to facilitate a movement of electrons away from the nanowire cores;
• and
• a second conducting electrode connected to the reduced graphene oxide shells at a second end of the nanowire core/shell structures and providing a second electrical pathway to facilitate a movement of positive charges away from the reduced graphene oxide shells.