Method to form a photovoltaic cell comprising a thin lamina

Abstract

A very thin photovoltaic cell is formed by implanting gas ions below the surface of a donor body such as a semiconductor wafer. Ion implantation defines a cleave plane, and a subsequent step exfoliates a thin lamina from the wafer at the cleave plane. A photovoltaic cell, or all or a portion of the base or emitter of a photovoltaic cell, is formed within the lamina. In preferred embodiments, the wafer is affixed to a receiver before the cleaving step. Electrical contact can be formed to both surfaces of the lamina, or to one surface only.

1 . A method for fabricating a photovoltaic cell, the method comprising:
 affixing a first surface of a first contiguous, monolithic semiconductor donor body to a receiver;   after the affixing step, cleaving a first lamina of semiconductor material from the first donor body, wherein the first lamina of semiconductor material includes the first surface and remains affixed to the receiver, and   fabricating the photovoltaic cell, wherein the first lamina of semiconductor material comprises at least a portion of the base or of the emitter, or both, of the photovoltaic cell.   
     
     
         2 . The method of  claim 1  wherein the contiguous, monolithic semiconductor donor body contains no void having a dimension larger than 200 angstroms. 
     
     
         3  The method of  claim 1  further comprising, before the affixing step, implanting one or more species of gas ions into the first donor body, wherein this implanting step defines a cleave plane for the cleaving step. 
     
     
         4 . The method of  claim 3  wherein the cleaving step creates a second surface of the lamina parallel to the first surface, the method further comprising, after the cleaving step, processing the second surface of the lamina to modify its surface roughness. 
     
     
         5 . The method of  claim 3  wherein the cleaving step creates a second surface of the lamina parallel to the first surface, the method further comprising, after the cleaving step, coating the second surface with a substantially transparent material having a refractive index different from the refractive index of the semiconductor material. 
     
     
         6 . The method of  claim 1  wherein the first lamina of semiconductor material is between about 1 and about 80 microns thick. 
     
     
         7 . The method of  claim 1  wherein the donor body is a silicon wafer. 
     
     
         8 . The method of  claim 7  wherein the donor body is a float-zone silicon wafer. 
     
     
         9 . The method of  claim 1  wherein the donor body is a multicrystalline wafer. 
     
     
         10 . The method of  claim 1  wherein the donor body is a germanium wafer. 
     
     
         11 . A method for fabricating a photovoltaic cell, the method comprising:
 doping at least portions of a first surface of a semiconductor wafer;   implanting hydrogen ions through the first surface;   affixing the first surface to a receiver; and   after the affixing step, cleaving a first semiconductor lamina from the semiconductor wafer, wherein the first lamina comprises the first surface, wherein the first surface is bonded to the receiver,   wherein current is generated within the first lamina when it is exposed to light.   
     
     
         12 . The method of  claim 11  wherein the first lamina is between about 1 and about 20 microns thick. 
     
     
         13 . The method of  claim 11  wherein the first lamina has a second surface parallel to the first, wherein the first surface or the second surface has a peak-to-valley surface roughness between about 600 and about 50000 angstroms. 
     
     
         14 . The method of  claim 11  further comprising, after the cleaving step, cleaving a second lamina from the semiconductor wafer, the second lamina having a thickness between about 1 and about 20 microns. 
     
     
         15 . The method of  claim 11  further comprising implanting helium ions through the first surface. 
     
     
         16 . The method of  claim 11  further comprising, before the affixing step, forming a metal layer on the first surface or on the receiver. 
     
     
         17 . The method of  claim 16  wherein the metal layer comprises titanium, aluminum, chromium, molybdenum, tantalum, zirconium, vanadium, or tungsten. 
     
     
         18 . A method for forming a photovoltaic cell, the method comprising:
 depositing a first layer of a first material on a first surface of a silicon wafer;   implanting one or more species of gas ions through the first surface to define a cleave plane;   affixing the wafer to a receiver at the first surface;   heating the wafer to exfoliate a lamina from the wafer along a cleave plane, wherein the lamina comprises the first surface and the lamina remains affixed to the receiver;   texturing the first surface or the second surface of the lamina.   
     
     
         19 . The method of  claim 18  wherein the first material is a metal. 
     
     
         20 . The method of  claim 18  wherein the first material is amorphous silicon. 
     
     
         21 . The method of  claim 18  wherein the first material is an antireflective layer. 
     
     
         22 . The method of  claim 18  wherein the first material is a transparent conductive oxide. 
     
     
         23 . The method of  claim 18  further comprising doping the first surface to a first conductivity type by diffusion doping.