Solar Cell and Process for Producing the Same

Abstract

A surface of a multicrystalline silicon substrate is etched with an alkaline aqueous solution in a condition so that a surface area-to-planar surface area ratio R is smaller than 1.1. A multiplicity of fine textures are formed over the irregularities by dry etching. This allows fine textures to be formed uniformly, and a solar cell with high efficiency can thus be produced.

1 - 6 . (canceled)  
     
     
         7 . A solar cell comprising: 
 a multicrystalline silicon substrate;    irregularities formed on a light-reception surface of the substrate; and    a multiplicity of textures formed on the irregularities, wherein the textures are smaller than the irregularities,    wherein a ratio r expressed as r=a/b, which is the ratio between the length a of a virtual line connecting individual peaks of the textures at a vertical cross section of the substrate and the length b of a straight line connecting the endpoints of the virtual line, is equal to or larger than 1 and smaller than 1.1.    
     
     
         8 . The solar cell according to  claim 7 , wherein the textures have a height and a width equal to or less than 2 μm, respectively.  
     
     
         9 . The solar cell according to  claim 7 , wherein the textures have a height and a width equal to or less than 1 μm, respectively.  
     
     
         10 . The solar cell according to  claim 7 , wherein the textures have a height-to-width aspect ratio (height/width) equal to or less than 2.  
     
     
         11 . The solar cell according to  claim 7 , wherein the irregularities are formed by etching with an alkaline aqueous solution.  
     
     
         12 . The solar cell according to  claim 7 , wherein the textures are formed by dry etching.  
     
     
         13 . The solar tell according to  claim 7 , further comprising an antireflective film provided on the light-reception surface of the substrate.  
     
     
         14 . The solar cell according to  claim 13 , wherein the antireflective film is provided on the textures on the substrate.  
     
     
         15 . The solar cell according to  claim 7 , further comprising an electrode provided on a surface of the substrate.  
     
     
         16 . The solar cell according to  claim 15 , wherein the electrode is provided on the light-reception surface of the substrate.  
     
     
         17 . A solar cell comprising: 
 a multicrystalline silicon substrate;    irregularities formed on a light-reception surface of the substrate; and    a multiplicity of textures formed on the irregularities, wherein the textures are smaller than the irregularities,    wherein a surface area-to-planar surface area ratio R of the substrate is larger than 1 and smaller than 1.1.    
     
     
         18 . The solar cell according to  claim 17 , 
 wherein a ratio r expressed as r=a/b, which is the ratio between the length a of a virtual line connecting individual peaks of the textures at a vertical cross section thereof and the length b of a straight line connecting the endpoints of the virtual line, is equal to or larger than 1 and smaller than 1.1.    
     
     
         19 . The solar cell according to  claim 17 , wherein the textures have a height and a width equal to or less than 2 μm, respectively.  
     
     
         20 . The solar cell according to  claim 17 , wherein the textures have a height and a width equal to or loss than 1 μm, respectively.  
     
     
         21 . The solar cell according to  claim 17 , wherein the textures have a height-to-width aspect ratio (height/width) equal to or less than 2.  
     
     
         22 . The solar cell according to  claim 17 , wherein the irregularities are formed by etching with an alkaline aqueous solution.  
     
     
         23 . The solar cell according to  claim 17 , wherein the textures are formed by dry etching.  
     
     
         24 . The solar cell according to  claim 17 , further comprising an antireflective film provided on the light-reception surface of the substrate.  
     
     
         25 . The solar cell according to  claim 24 , wherein the antireflective film is provided on the textures on the substrate.  
     
     
         26 . The solar cell according to  claim 17 , further comprising an electrode provided on a surface of the substrate.  
     
     
         27 . The solar cell according to  claim 26 , wherein the electrode is provided on the light-reception surface of the substrate.  
     
     
         28 . A process for producing a solar cell, comprising; 
 a step of forming irregularities on a surface of a light-reception surface of a multicrystalline silicon substrate by etching; and    a step of forming multiplicity of textures on the irregularities, wherein the textures are smaller than the irregularities,    wherein in the step of forming multiplicity of textures, a ratio r expressed as r=a/b, which is the ratio between the length a of a virtual line connecting individual peaks of the textures at a vertical cross section thereof and the length b of a straight line connecting the endpoints of the virtual line, is equal to or larger than 1 and smaller than 1.1.    
     
     
         29 . The process for producing a solar cell according to  claim 28 , wherein the irregularities are formed by etching with an alkaline aqueous solution, and the textures are formed by dry etching.  
     
     
         30 . The process for producing a solar cell according to  claim 28 , further comprising a step of providing an antireflective film on the light-reception surface of the substrate.  
     
     
         31 . The process for producing a solar cell according to  claim 30 , wherein the antireflective film is provided on the textures on the substrate.  
     
     
         32 . The process for producing a solar cell according to  claim 28 , further comprising a step of providing an electrode on a surface of the substrate.  
     
     
         33 . The process for producing a solar cell according to  claim 32 , wherein the electrode is provided on the light-reception surface of the substrate.  
     
     
         34 . A process for producing a solar cell, comprising: 
 a step of forming irregularities on a surface of a light-reception surface of a multicrystalline silicon substrate by etching, wherein a surface area-to-planar surface area ratio R is larger than 1 and smaller than 1.1,    a step of forming multiplicity of textures on the irregularities, wherein the textures are smaller than the irregularities.    
     
     
         35 . The process for producing a solar cell according to  claim 34 , wherein the irregularities are formed by etching with an alkaline aqueous solution, and the textures are formed by dry etching.  
     
     
         36 . The process for producing a solar cell according to  claim 34 , further comprising a step of providing an antireflective film on the light-reception surface of the substrate.  
     
     
         37 . The process for producing a solar cell according to  claim 36 , wherein the antireflective film is provided on the textures on the substrate.  
     
     
         38 . The process or producing a solar cell according to  claim 34 , further comprising a step of providing an electrode on a surface of the substrate.  
     
     
         39 . The process for producing a solar cell according to  claim 38 , wherein the electrode is provided on the light-reception surface of the substrate.