Photovoltaic devices with an interfacial band-gap modifying structure and methods for forming the same

Abstract

A Schottky-barrier-reducing layer is provided between a p-doped semiconductor layer and a transparent conductive material layer of a photovoltaic device. The Schottky-barrier-reducing layer can be a conductive material layer having a work function that is greater than the work function of the transparent conductive material layer. The conductive material layer can be a carbon-material layer such as a carbon nanotube layer or a graphene layer. Alternately, the conductive material layer can be another transparent conductive material layer having a greater work function than the transparent conductive material layer. The reduction of the Schottky barrier reduces the contact resistance across the transparent material layer and the p-doped semiconductor layer, thereby reducing the series resistance and increasing the efficiency of the photovoltaic device.

What is claimed is: 
     
         1 . A photovoltaic device comprising a stack, from one side to another side, of a transparent conductive material layer, a Schottky-barrier-reducing layer contacting said transparent conductive material layer, and a p-doped semiconductor layer, wherein a Schottky barrier across said stack has a lower contact resistance than a Schottky barrier across a comparative exemplary stack that includes all layers of said stack less said Schottky-barrier-reducing layer, wherein said Schottky-barrier-reducing layer is an optically transparent layer including an allotrope of carbon and is in direct contact with said p-doped semiconductor layer and is in direct contact with said transparent conductive material layer, wherein said Schottky-barrier-reducing layer includes a same material as said transparent conductive material layer and has a different doping than said transparent conductive material layer. 
     
     
         2 . The photovoltaic device of  claim 1 , wherein said transparent conductive material layer includes an aluminum-doped zinc oxide having an aluminum doping at a first dopant concentration, and said Schottky-barrier-reducing layer includes an aluminum-doped zinc oxide having an aluminum doping at a second dopant concentration, wherein said first dopant concentration is greater than said second dopant concentration. 
     
     
         3 . The photovoltaic device of  claim 1 , wherein said transparent conductive material layer includes a first fluorine-doped tin oxide having a fluorine doping at a first dopant concentration, and said Schottky-barrier-reducing layer includes a second fluorine-doped tin oxide having a fluorine doping at a second dopant concentration, wherein said first dopant concentration is greater than said second dopant concentration. 
     
     
         4 . The photovoltaic device of  claim 1 , wherein said Schottky-barrier-reducing layer includes a material having a higher resistivity than a material of said transparent conductive material layer. 
     
     
         5 . The photovoltaic device of  claim 1 , wherein said Schottly-barrier-reducing layer has a work function that is greater than a work function of said transparent conductive material layer and is lesser than an absolute value of a Fermi level of said p-doped semiconductor layer. 
     
     
         6 . The photovoltaic device of  claim 1 , wherein a series resistance of said photovoltaic device is equal to or less than 9 Ohms-cm 2 . 
     
     
         7 . The photovoltaic device of  claim 1 , wherein said p-doped semiconductor layer includes a hydrogenated p-doped semiconductor-containing material. 
     
     
         8 . The photovoltaic device of  claim 1 , further comprising:
 an intrinsic semiconductor layer contacting said p-doped semiconductor layer; and   an n-doped semiconductor layer contacting said intrinsic semiconductor layer.   
     
     
         9 . The photovoltaic device of  claim 8 , wherein said intrinsic semiconductor layer includes a hydrogenated amorphous intrinsic semiconductor material. 
     
     
         10 . The photovoltaic device of  claim 8 , wherein said n-doped semiconductor layer includes hydrogenated n-doped amorphous semiconductor material. 
     
     
         11 . The photovoltaic device of  claim 8 , further comprising at least one back reflector layer located on said n-doped semiconductor layer. 
     
     
         12 . A method of forming a photovoltaic device comprising:
 forming a transparent conductive material layer on a substrate;   forming a Schottky-barrier-reducing layer on said transparent conductive material layer, wherein said Schottky-barrier-reducing layer includes a same material as said transparent conductive material layer and has a different doping than said transparent conductive material layer; and   forming a p-doped semiconductor layer on said Schottky-barrier-reducing layer, wherein a Schottky barrier across a stack of said transparent conductive material layer, said Schottky-barrier-reducing layer, and said p-doped semiconductor layer has less contact resistance than a Schottky barrier across another stack that includes all layers of said stack less said Schottky-barrier-reducing layer.   
     
     
         13 . The method of  claim 12 , wherein said transparent conductive material layer includes an aluminum-doped zinc oxide having an aluminum doping at a first dopant concentration, and said Schottky-barrier-reducing layer includes an aluminum-doped zinc oxide having an aluminum doping at a second dopant concentration, wherein said first dopant concentration is greater than said second dopant concentration. 
     
     
         14 . The method of  claim 12 , wherein said transparent conductive material layer includes a first fluorine-doped tin oxide having a fluorine doping at a first dopant concentration, and said Schottky-barrier-reducing layer includes a second fluorine-doped tin oxide having a fluorine doping at a second dopant concentration, wherein said first dopant concentration is greater than said second dopant concentration. 
     
     
         15 . The method of  claim 12 , wherein said Schottky-barrier-reducing layer includes a material having a higher resistivity than a material of said transparent conductive material layer. 
     
     
         16 . The method of  claim 12 , wherein said Schottky-barrier-reducing layer has a work function that is greater than a work function of said transparent conductive material layer and is lesser than an absolute value of a Fermi level energy of said p-doped semiconductor layer. 
     
     
         17 . The method of  claim 12 , further comprising:
 forming an intrinsic semiconductor layer on said p-doped semiconductor layer; and   forming an n-doped semiconductor layer on said intrinsic semiconductor layer.   
     
     
         18 . The method of  claim 17 , wherein said intrinsic semiconductor layer includes a hydrogenated amorphous intrinsic semiconductor material. 
     
     
         19 . The method of  claim 17 , wherein said n-doped semiconductor layer includes hydrogenated n-doped amorphous semiconductor material. 
     
     
         20 . The method of  claim 17 , further comprising forming at least one back reflector layer on said n-doped semiconductor layer.