Solar cell employing an enhanced free hole density p-doped material and methods for forming the same

Abstract

A p-doped semiconductor layer of a photovoltaic device is formed employing an inert gas within a carrier gas. The presence of the inert gas within the carrier gas increases free hole density within the p-doped semiconductor layer. This decreases the Schottky barrier at an interface with a transparent conductive material layer, thereby significantly reducing the series resistance of the photovoltaic device. The reduction of the series resistance increases the open-circuit voltage, the fill factor, and the efficiency of the photovoltaic device. This effect is more prominent if the p-doped semiconductor layer is also doped with carbon, and has a band gap greater than 1.85V. The p-doped semiconductor material of the p-doped semiconductor layer can be hydrogenated if the carrier gas includes a mix of H 2 and the inert gas.

1 . A method of forming a photovoltaic device comprising:
 forming a transparent conductive material layer on a substrate; and   forming a p-doped semiconductor layer on said transparent conductive material layer in the presence of a semiconductor-material-containing reactant and a carrier gas including an inert gas.   
     
     
         2 . The method of  claim 1 , wherein said p-doped semiconductor layer is microcrystalline. 
     
     
         3 . The method of  claim 1 , wherein said p-doped semiconductor layer includes a silicon-containing material. 
     
     
         4 . The method of  claim 3 , wherein said p-doped semiconductor layer includes a silicon-carbon alloy material, wherein an atomic concentration of carbon is from 1% to 90%. 
     
     
         5 . The method of  claim 1 , wherein said p-doped semiconductor layer includes a material having a band gap from 1.8 eV to 3.5 eV. 
     
     
         6 . The method of  claim 1 , wherein said carrier gas includes said inert gas and H 2 . 
     
     
         7 . The method of  claim 6 , wherein said inert gas is He. 
     
     
         8 . The method of  claim 1 , wherein said semiconductor-material-containing reactant includes at least one of SiH 4 , Si 2 H 6 , SiH 2 Cl 2 , SiHCl 3 , SiCl 4 , GeH 4 , Ge 2 H 6 , GeH 2 Cl 2 , and GeCl 4 . 
     
     
         9 . The method of  claim 1 , wherein said p-doped semiconductor layer is formed in a continuous or intermittent presence of a carbon-containing gas. 
     
     
         10 . The method of  claim 1 , wherein said p-doped semiconductor layer is formed in a chemical vapor deposition. 
     
     
         11 . The method of  claim 1 , wherein said p-doped semiconductor layer is formed by plasma-enhanced chemical vapor deposition at a deposition temperature from 50° C. to 400° C. 
     
     
         12 . The method of  claim 1 , 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.   
     
     
         13 . The method of  claim 12 , further comprising forming at least one back reflector layer on said n-doped semiconductor layer. 
     
     
         14 . The method of  claim 13 , wherein said at least one back reflector layer includes another transparent conductive material layer and a metallic layer. 
     
     
         15 . The method of  claim 1 , wherein said transparent conductive material layer is a doped zinc oxide layer. 
     
     
         16 . The method of  claim 1 , wherein said substrate is optically transparent. 
     
     
         17 . A photovoltaic device comprising:
 a transparent conductive material layer;   a p-doped semiconductor layer contacting said transparent conductive material layer;   an intrinsic semiconductor layer contacting said p-doped semiconductor layer; and   an n-doped semiconductor layer contacting said intrinsic semiconductor layer, wherein a series resistance of said photovoltaic device is equal to, or less than, 9 Ohms-cm 2 .   
     
     
         18 . The photovoltaic device of  claim 17 , wherein said transparent conductive material layer includes an aluminum-doped zinc oxide material. 
     
     
         19 . The photovoltaic device of  claim 17 , wherein said p-doped semiconductor layer includes a p-doped microcrystalline silicon-carbon alloy. 
     
     
         20 . The photovoltaic device of  claim 19 , wherein an open-circuit voltage of said photovoltaic device is greater than 900 mV. 
     
     
         21 . The photovoltaic device of  claim 19 , wherein a band gap of said p-doped semiconductor layer is greater than 1.85 eV, and a fill factor of said photovoltaic device is greater than 60%. 
     
     
         22 . The photovoltaic device of  claim 19 , wherein a band gap of said p-doped semiconductor layer is greater than 1.85 eV, and efficiency of said photovoltaic device is greater than 8%. 
     
     
         23 . The photovoltaic device of  claim 19 , wherein said p-doped microcrystalline silicon-carbon alloy includes a microcrystalline hydrogenated p-doped silicon-carbon alloy. 
     
     
         24 . The photovoltaic device of  claim 17 , wherein said intrinsic semiconductor layer includes hydrogenated amorphous intrinsic silicon. 
     
     
         25 . The photovoltaic device of  claim 17 , wherein said n-doped semiconductor layer includes hydrogenated amorphous n-doped silicon.