Photovoltaic Cell Comprising A Thin Lamina Having A Rear Junction And Method Of Making

Abstract

Fabrication of a photovoltaic cell comprising a thin semiconductor lamina may require additional processing after the semiconductor lamina is bonded to a receiver. To minimize high-temperature steps after bonding, the p-n junction is formed at the back of the cell, at the bonded surface. In some embodiments, the front surface of the semiconductor lamina is not doped or is locally doped using low-temperature methods. The base resistivity of the photovoltaic cell may be reduced, allowing a front surface field to be reduced or omitted.

What is claimed is: 
     
         1 . A photovoltaic cell comprising a semiconductor lamina, the semiconductor lamina having a front surface and a back surface, wherein
 incident light enters the semiconductor lamina at the front surface during normal operation of the photovoltaic cell,   the body of the semiconductor lamina is doped to a first conductivity type,   the back surface of the semiconductor lamina is heavily doped to a second conductivity type opposite the first conductivity type, and   no more than ten percent of the surface area of the front surface of the semiconductor lamina is doped more heavily to the first conductivity type than the lamina body.   
     
     
         2 . The photovoltaic cell of  claim 1 , wherein a thickness of the semiconductor lamina, measured perpendicularly between the front surface and the back surface, is less than about 80 microns. 
     
     
         3 . The photovoltaic cell of  claim 2 , wherein the thickness is between about 0.2 microns and about 10 microns. 
     
     
         4 . The photovoltaic cell of  claim 1 , wherein the semiconductor lamina consists essentially of at least one of monocrystalline, polycrystalline, and multicrystalline silicon. 
     
     
         5 . The photovoltaic cell of  claim 1 , wherein substantially no portion of the front surface is doped more heavily to the first conductivity type than the lamina body. 
     
     
         6 . The photovoltaic cell of  claim 5  wherein, within about 300 nm of the front surface of the semiconductor lamina, no portion of the semiconductor lamina has a dopant concentration greater than about 1×10 19  atoms/cm 3 . 
     
     
         7 . The photovoltaic cell of  claim 1 , wherein the front surface of the semiconductor lamina comprises a plurality of discrete regions doped more heavily than the lamina body, and wherein the combined area of the more heavily doped regions is not more than about ten percent of the surface area of the front surface. 
     
     
         8 . The photovoltaic cell of  claim 7 , wherein each more heavily doped region of the plurality is in electrical contact with a conductive material. 
     
     
         9 . The photovoltaic cell of  claim 1 , further comprising a layer of a charged dielectric of the second conductivity type located on or above the first surface. 
     
     
         10 . The photovoltaic cell of  claim 9 , wherein the first conductivity type is n-type and the charged dielectric is silicon nitride. 
     
     
         11 . The photovoltaic cell of  claim 9 , wherein the first conductivity type is p-type. 
     
     
         12 . The photovoltaic cell of  claim 11 , wherein the charged dielectric is alumina.