Solar cells having nanowires and methods of fabricating nanowires

Abstract

A solar cell includes a plurality of nanowires arranged such that diameters of the nanowires sequentially increase in a first direction along a path of incident light. In a method of forming nanowires, a catalyst layer is formed on a substrate, a plurality of nanoparticles are formed by thermally processing the catalyst layer, and nanowires are grown from the plurality of nanoparticles. The catalyst layer has a thickness that increases in a first direction, and the plurality of nanoparticles have diameters that increase in the first direction.

1 - 8 . (canceled) 
     
     
         9 . A method of forming nanowires, the method comprising:
 forming a catalyst layer on a substrate, the catalyst layer having a thickness that increases in a first direction;   forming a plurality of nanoparticles by thermally processing the catalyst layer, the nanoparticles having diameters that increase in the first direction; and   growing a plurality of nanowires from the plurality of nanoparticles.   
     
     
         10 . The method of  claim 9 , wherein the grown plurality of nanowires are arranged such that the diameters of the plurality of nanowires sequentially increase in the first direction. 
     
     
         11 . The method of  claim 9 , wherein a surface of the substrate on which the catalyst layer is formed is one of vertical and tilted with respect to a top surface of a base unit supporting the substrate. 
     
     
         12 . The method of  claim 9 , wherein the catalyst layer is faulted on a tilted surface of the substrate. 
     
     
         13 . The method of  claim 9 , wherein the catalyst layer is formed by using one of an electron beam deposition method and a sputtering method. 
     
     
         14 . The method of  claim 9 , further comprising:
 forming a buffer layer on the substrate, the buffer layer having a thickness that sequentially decreases in the first direction; wherein the forming of the catalyst layer includes,   forming a catalyst material layer having a uniform thickness on the buffer layer, and   forming the catalyst layer having a thickness that sequentially increases in the first direction by forming a compound layer via reaction between the buffer layer and the catalyst material layer.   
     
     
         15 . The method of  claim 9 , wherein the catalyst layer is thermally processed within a temperature range between about 300° C. and about 600° C., inclusive. 
     
     
         16 . The method of  claim 9 , wherein the plurality of nanowires are grown by using a chemical vapor deposition (CVD) method. 
     
     
         17 . The method of  claim 9 , wherein the plurality of nanowires are grown to have diameters between about 1 nm and about 1 μm, inclusive. 
     
     
         18 . The method of  claim 9 , wherein the plurality of nanowires include one of nanotubes and nanorods.