Three-dimensional solar cell having increased efficiency

Abstract

A nano-scale tower structure array having increased surface area on each tower for gathering incident light is provided for use in three-dimensional solar cells. Embodiments enhance surface roughness of each tower structure to increase the surface area available for light gathering. Enhanced roughness can be provided by manipulating passivation layer etching parameters used during a formation process of the nano-scale tower structures, in order to affect surface roughness of a photoresist layer used for the etch. Manipulable etching parameters can include power, gas pressure, and etching compound chemistry.

What is claimed is: 
     
         1 - 8 . (canceled) 
     
     
         9 . A three-dimensional photovoltaic device comprising:
 a plurality of tower structures having a photovoltaic coating along a top and sidewalls of each tower structure, wherein
 the sidewalls of each tower structure have a surface roughness providing a selected level of scattering of light incident on the tower structures, and 
 each tower structure has a conductive core material; 
   a conductive layer formed over a substrate, wherein
 the conductive core material of each tower structure is coupled to the conductive layer; and 
   a passivation layer formed over the conductive layer.   
     
     
         10 . The three-dimensional photovoltaic device of  claim 9 , wherein the plurality of tower structures are formed by a process comprising:
 forming the passivation layer over the conductive layer;   forming a photoresist layer over the passivation layer;   patterning the photoresist layer for a plurality of holes;   etching the passivation layer to form the plurality of holes, wherein
 said etching is performed such that a sidewall of each of the plurality of holes through the photoresist layer has a surface roughness; 
   forming the conductive core material in the one or more holes through both the passivation layer and the photoresist layer, and   removing the photoresist layer.   
     
     
         11 . The three-dimensional photovoltaic device of  claim 10  wherein the surface roughness of the holes provides the selected level of scattering of light incident on the tower structures. 
     
     
         12 . The three-dimensional photovoltaic device of  claim 9  wherein a tower structure of the plurality of tower structures is approximately 10 microns in height over the conductive layer and approximately 4 microns in diameter. 
     
     
         13 . The three-dimensional photovoltaic device of  claim 12  wherein the surface roughness of the tower structure is between 0.1 and 1.6 microns. 
     
     
         14 . The three-dimensional photovoltaic device of  claim 9  wherein the conductive core material comprises one of a metal or a metal alloy. 
     
     
         15 . The three-dimensional photovoltaic device of  claim 14  wherein the conductive core material comprises nickel or zinc. 
     
     
         16 . The three-dimensional photovoltaic device of  claim 9  further comprising:
 a passivation layer formed over the conductive layer. 
 
     
     
         17 . The three-dimensional photovoltaic device of  claim 9  wherein the photovoltaic coating is one of CdTe or CdS.