Grain growth for solar cells

Abstract

A solar cell can include a silicon layer formed over a silicon substrate. The silicon layer can have a P-type doped region and an N-type doped region. Portions of the silicon layer can have a grain size larger than other portions of the silicon layer. For example, larger grains of the silicon layer formed within a depletion region between P-type and N-type doped regions can minimize recombination loss at the P-type and N-type doped region boundaries and improve solar cell efficiency.

What is claimed is: 
     
         1 . A solar cell, comprising:
 a semiconductor substrate having upper regions, angled regions and lower regions; and   a semiconductor layer above the semiconductor substrate, the semiconductor layer having a doped region of a first conductivity type and a doped region of a second conductivity type, wherein portions of the semiconductor layer over upper regions and lower regions of the semiconductor substrate have a larger grain size than portions of the semiconductor layer over angled regions of the semiconductor substrate.   
     
     
         2 . The solar cell of  claim 1 , wherein the larger grains are disposed at a depletion region of the semiconductor layer, the depletion region between the doped region of the first conductivity type and the doped region of the second conductivity type. 
     
     
         3 . The solar cell of  claim 1 , wherein the semiconductor layer is a polycrystalline semiconductor layer. 
     
     
         4 . The solar cell of  claim 1 , wherein the total average grain size of the semiconductor layer is greater than or equal to 1 μm. 
     
     
         5 . The solar cell of  claim 1 , wherein the larger grains are disposed adjacent to the portions of the semiconductor layer over the angled regions of the semiconductor substrate and the larger grains are disposed adjacent to the portions of the semiconductor layer over the upper and lower regions of the semiconductor substrate. 
     
     
         6 . The solar cell of  claim 1 , wherein the upper regions of the semiconductor substrate and the lower regions of the semiconductor substrate have planes that are substantially parallel with one another. 
     
     
         7 . The solar cell of  claim 1 , wherein the doped region of the first conductivity type and the doped region of the second conductivity type abut in a contiguous portion of the semiconductor layer. 
     
     
         8 . The solar cell of  claim 1 , further comprising:
 a dielectric layer between the semiconductor layer and the semiconductor substrate.   
     
     
         9 . A solar cell, comprising:
 a silicon substrate having upper regions, angled regions and lower regions; and   a silicon layer above the silicon substrate, the silicon layer having a P-type doped region and an N-type doped region, wherein portions of the silicon layer over upper regions and lower regions of the silicon substrate have a larger grain size than portions of the silicon layer over angled regions of the silicon substrate, the larger grains disposed at a depletion region of the silicon layer, the depletion region between the P-type doped region and the N-type doped region.   
     
     
         10 . The solar cell of  claim 9 , wherein the silicon layer is a polycrystalline silicon layer. 
     
     
         11 . The solar cell of  claim 9 , wherein the total average grain size of the silicon layer is greater than or equal to 1 μm. 
     
     
         12 . The solar cell of  claim 9 , wherein the larger grains are disposed adjacent to the portions of the silicon layer over the angled regions of the silicon substrate and the larger grains are disposed adjacent to the portions of the silicon layer over the upper and lower regions of the silicon substrate. 
     
     
         13 . The solar cell of  claim 9 , wherein the upper regions of the silicon substrate and the lower regions of the silicon substrate have planes that are substantially parallel with one another. 
     
     
         14 . The solar cell of  claim 9 , wherein the P-type doped region and the N-type doped region abut in a contiguous portion of the silicon layer. 
     
     
         15 . The solar cell of  claim 9 , further comprising:
 a dielectric layer between the silicon layer and the silicon substrate.   
     
     
         16 . A solar cell, comprising:
 a silicon substrate having upper regions, angled regions and lower regions; and   a silicon layer above the silicon substrate, the silicon layer having a P-type doped region and an N-type doped region, wherein portions of the silicon layer over upper regions and lower regions of the silicon substrate have a larger grain size than portions of the silicon layer over angled regions of the silicon substrate, the larger grains disposed at a contiguous portion of the silicon layer, the contiguous portion between the P-type doped region and the N-type doped region.   
     
     
         17 . The solar cell of  claim 16 , wherein the total average grain size of the silicon layer is greater than or equal to 1 μm. 
     
     
         18 . The solar cell of  claim 16 , wherein the larger grains are disposed adjacent to the portions of the silicon layer over the angled regions of the silicon substrate and the larger grains are disposed adjacent to the portions of the silicon layer over the upper and lower regions of the silicon substrate. 
     
     
         19 . The solar cell of  claim 16 , wherein the upper regions of the silicon substrate and the lower regions of the silicon substrate have planes that are substantially parallel with one another. 
     
     
         20 . The solar cell of  claim 16 , further comprising:
 a dielectric layer between the silicon layer and the silicon substrate.