Thin Film Solar Cell with Ceramic Handling Layer

Abstract

A solar cell may comprise a stack of thin continuous epitaxial single crystal solar cell layers on a single crystal wafer, and a handling layer on the stack, the handling layer having a waffle-shaped structure with an array of either square or circular apertures, wherein the handling layer includes electrical contacts to the stack. The solar cell may comprise a boundary layer between the stack and the handling layer, the boundary layer being attached to both the stack and the handling layer, and the boundary layer being greater than 10 nanometers thick and parallel to the layers in the stack. The waffle-shaped structure may include perpendicular sets of first and second parallel ridges, wherein at least one of the sets is aligned at a small angle to a cleavage plane of the single crystal wafer.

What is claimed is: 
     
         1 . A solar cell comprising:
 a stack of thin single crystal solar cell layers;   a handling layer; and   a boundary layer between said stack and said handling layer, said boundary layer being attached to both said stack and said handling layer, said boundary layer being greater than 10 nanometers thick and parallel to the layers in said stack.   
     
     
         2 . The solar cell as in  claim 1 , wherein said handling layer has a coefficient of thermal expansion greater than or equal to the coefficient of thermal expansion of said stack over a temperature range from ambient temperatures to a maximum temperature, said maximum temperature being the highest temperature reached during the forming of said handling layer. 
     
     
         3 . The solar cell as in  claim 1 , wherein said handling layer has a coefficient of thermal expansion in the range from 5% less than to 25% greater than the coefficient of thermal expansion of said stack over a temperature range from ambient temperatures to a maximum temperature, said maximum temperature being the highest temperature reached during the forming of said handling layer. 
     
     
         4 . The solar cell as in  claim 1 , wherein said handling layer reflects back into said stack visible light passing through said stack towards said handling layer. 
     
     
         5 . The solar cell as in  claim 1 , wherein the interface between said handling layer and said boundary layer reflects visible light passing through said stack back into said stack. 
     
     
         6 . The solar cell as in  claim 1 , further comprising electrical contacts at the interface between said stack and said handling layer. 
     
     
         7 . The solar cell as in  claim 6 , wherein said handling layer comprises metallic vias configured to provide electrical connections to said electrical contacts. 
     
     
         8 . The solar cell as in  claim 1 , wherein said handling layer has a waffle-shaped structure with a first set of ridges and a second set of ridges, said first set of ridges being perpendicular to said second sets of ridges. 
     
     
         9 . The solar cell as in  claim 8 , wherein at least one of said first and second sets of ridges are aligned at a small angle to a cleavage plane of said stack of thin single crystal solar cell layers. 
     
     
         10 . The solar cell as in  claim 9 , wherein said cleavage plane is the 100 family of planes. 
     
     
         11 . The solar cell as in  claim 9 , wherein said small angle is in the range between 3 and 10 degrees. 
     
     
         12 . The solar cell as in  claim 1 , wherein said handling layer has a waffle-shaped structure with an array of roughly square apertures. 
     
     
         13 . The solar cell as in  claim 12 , wherein the square apertures are roughly less than 500 microns on a side. 
     
     
         14 . The solar cell as in  claim 1 , wherein said handling layer has a waffle-shaped structure with an array of circular apertures. 
     
     
         15 . The solar cell as in  claim 1 , wherein said boundary layer is selected from the group consisting of a silicon oxide layer, a silicon nitride layer and an alumina layer.