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

Abstract

A photovoltaic solar cell apparatus is described herein combining the advantages of several discoveries that address the previously unsolved problem of creating high conversion efficiency solar cells at a low cost. The solar cell designs and underlying principals disclosed herein may be applied in any type of photovoltaic solar power application, such as large scale photovoltaic solar plants, rooftop panels, solar powered electronic devices, and many others.

1 - 93 . (canceled) 
     
     
         94 . 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.   
     
     
         95 - 100 . (canceled) 
     
     
         101 . The method according to  claim 94 , wherein the plurality of nanowire cores comprises surface annealed nanowires cores. 
     
     
         102 - 110 . (canceled) 
     
     
         111 . The method according to  claim 94 , wherein the nanowire cores include a dopant along at least a portion of the longitudinal surface thereof. 
     
     
         112 - 115 . (canceled) 
     
     
         116 . The method according to  claim 94 , wherein second conducting electrode is at least partially transparent to sunlight. 
     
     
         117 - 125 . (canceled) 
     
     
         126 . 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.   
     
     
         127 - 132 . (canceled) 
     
     
         133 . The photovoltaic solar cell apparatus according to  claim 126 , wherein the thermal reduction of graphene oxide to reduced graphene oxide is performed in an atmosphere comprising at least 10% hydrogen. 
     
     
         134 . The photovoltaic solar cell apparatus according to  claim 133 , wherein thermal reduction of graphene oxide to reduced graphene oxide is performed at a temperature of between about 250° C. to 350° C. 
     
     
         135 . The photovoltaic solar cell apparatus according to  claim 126 , wherein prior to the step of surrounding the plurality of zinc oxide nanowire cores with graphene oxide, the plurality of nanowire cores are subjected to a post-growth annealing process to reduce structural defects at the surface of the nanowires cores. 
     
     
         136 . (canceled) 
     
     
         137 . The photovoltaic solar cell apparatus according to  claim 126 , wherein the step of surrounding the plurality of nanowire cores with graphene oxide comprises a coating technique. 
     
     
         138 . The photovoltaic solar cell apparatus according to  claim 137 , wherein the coating technique is at least one of drop coating, dip coating or spin coating. 
     
     
         139 - 149 . (canceled) 
     
     
         150 . The photovoltaic solar cell apparatus according to claim  26 , wherein second conducting electrode is at least partially to transparent to sunlight. 
     
     
         151 - 160 . (canceled) 
     
     
         161 . 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.   
     
     
         162 . The photovoltaic solar cell apparatus according to  claim 161 , wherein the substantially continuous coating of a nonconductive material on the foil substrate comprises zinc oxide. 
     
     
         163 - 167 . (canceled) 
     
     
         168 . The photovoltaic solar cell apparatus according to any one of  claims 161   167   claim 161 , wherein the plurality of nanowire cores comprises surface annealed nanowires cores. 
     
     
         169 - 176 . (canceled) 
     
     
         177 . The photovoltaic solar cell apparatus according to  claim 161 , wherein the nanowire cores include a dopant along at least a portion of the longitudinal surface thereof. 
     
     
         178 . The photovoltaic solar cell apparatus according to  claim 177 , wherein the dopant comprises at least one of aluminum, indium, chlorine, and gallium. 
     
     
         179 . The photovoltaic solar cell apparatus according to  claim 161 , wherein the reduced graphene shells include an n-type dopant. 
     
     
         180 . The photovoltaic solar cell apparatus according to  claim 179 , wherein the n-type dopant comprises nitrogen. 
     
     
         181 . (canceled) 
     
     
         182 . The photovoltaic solar cell apparatus according to  claim 161 , wherein second conducting electrode is at least partially transparent to sunlight. 
     
     
         183 - 184 . (canceled) 
     
     
         185 . The photovoltaic solar cell apparatus according to  claim 182 , wherein second conducting electrode comprises at least one of indium tin oxide, graphene, or reduced graphene oxide. 
     
     
         186 - 191 . (canceled)