Photovoltaic cell

Abstract

A photovoltaic cell having an electrically conductive substrate, which may be glass having a film of conductive tin oxide; a first layer containing a suitable semiconductor, which layer has a first component film with an amorphous structure and a second component film with a polycrystalline structure; a second layer forming a heterojunction with the first layer; and suitable electrodes where the heterojunction is formed from a solution containing copper, the amorphous film component is superposed above an electrically conductive substrate to resist permeation of the copper-containing material to shorting electrical contact with the substrate. The penetration resistant amorphous layer permits a variety of processes to be used in forming the heterojunction with even very thin layers (1-6μ thick) of underlying polycrystalline semi-conductor materials. In some embodiments, the amorphous-like structure may be formed by the addition of aluminum or zirconium compounds to a solution of cadmium salts sprayed over a heated substrate.

What is claimed is: 
     
       1. A photovoltaic cell, comprising an electrically conductive substrate,   a first layer containing CdS,   a second layer of Cu x  S superposed on said first layer and forming a photovoltaic heterojunction therewith, and   an electrode contacting said second layer,   said first layer containing a compound of a selected metal in an amount effective to provide at least a portion of said CdS in said first layer with an amorphous structure resistant to permeation by said Cu x  S through said first layer to said electrically conductive substrate.   
     
     
       2. A photovoltaic cell according to claim 1, wherein said compound of said selected metal is formed from a solution containing a cadmium compound and a salt of said selected metal, said selected metal being at least 10 molar percent of the total metal content of said solution.   
     
     
       3. A photovoltaic cell according to claim 1 or claim 2, wherein said compound of said selected metal is included in the greatest amount in said first layer adjacent said electrically conductive substrate and in the least amount in said first layer remote from said electrically conductive substrate. 
     
     
       4. A photovoltaic cell according to claim 1 or claim 2, wherein said first layer includes a first film component containing CdS and said compound of said selected metal, and   a second film component containing, polycrystalline CdS.   
     
     
       5. A photovoltaic cell according to claim 4, wherein said first and second film components are each formed to a thickness of 1-4 microns. 
     
     
       6. A photovoltaic cell according to claim 5, wherein said selected metal is from the group consisting of aluminum and zirconium. 
     
     
       7. A photovoltaic cell, comprising an electrically conductive substrate   a first layer containing CdS,   a second layer of Cu x  S superposed on said first layer and forming a photovoltaic heterojunction therewith, and   an electrode contacting said second layer,   said first layer containing a compound of aluminum or zirconium in an amount effective to provide at least a portion of said CdS in said first layer with an amorphous structure resistant to permeation by said Cu x  S through said first layer to said electrically conductive substrate.   
     
     
       8. A photovoltaic cell according to claim 7, wherein said compound of said aluminum or zirconium is formed from a solution containing a cadmium compound and a salt of said aluminum or zirconium, the aluminum or zirconium content being at least 10 molar percent of the total metal content of said solution. 
     
     
       9. A photovoltaic cell according to claim 7 or claim 8, wherein said compound of said selected metal is included in the greatest amount in said first layer adjacent said electrically conductive substrate and in the least amount in said first layer remote from said electrically conductive substrate. 
     
     
       10. A photovoltaic cell according to claim 7 or claim 8, wherein said first layer includes a first film component containing CdS and said compound of said aluminum or zirconium, and   a second film component containing polycrystalline CdS.   
     
     
       11. A photovoltaic cell according to claim 10, wherein said first and second film components are each formed to a thickness of 1-4 microns. 
     
     
       12. In a photovoltaic cell having an electrically conductive substrate, a first layer containing CdS, a second layer of Cu x  S superposed on said first layer and forming a photovoltaic heterojunction therewith, and an electrode contacting said second layer, an improved first layer comprising a compound of a selected metal in an amount effective to provide at least a portion of said CdS in said first layer with an amorphous structure resistant to permeation by said Cu x  S through said first layer to said electrically conductive substrate.   
     
     
       13. A photovoltaic cell according to claim 12, wherein said compound of said selected metal is formed from a solution containing a cadmium compound and a salt of said selected metal, said selected metal being at least 10 molar percent of the total metal content of said solution.   
     
     
       14. A photovoltaic cell according to claim 12 or claim 13, wherein said compound of said selected metal is included in the greatest amount in said first layer adjacent said electrically conductive substrate and in the least amount in said first layer remote from said electrically conductive substrate. 
     
     
       15. A photovoltaic cell according to claim 12 or claim 13, wherein said first layer includes a first film component containing CdS and said compound of said selected metal, and   a second film component containing polycrystalline CdS.   
     
     
       16. A photovoltaic cell according to claim 15, wherein said first and second film component layers are each formed to a thickness of 1-4 microns. 
     
     
       17. A photovoltaic cell according to claim 16, wherein said selected metal is from the group consisting of aluminum and zirconium. .Iadd. 18. An improved photovoltaic cell having an electrically conductive base, a first layer of polycrystalline semiconductor material, a second layer of material forming a heterojunction with said semiconductor material, and an electrode contacting said second layer, wherein the improvement comprises: said first layer of semiconductor material having a portion which is resistant to permeation through said first layer to said base by materials forming said heterojunction. .Iaddend..Iadd. 19. An improved photovoltaic cell according to claim 18, wherein said first layer varies from a first material structure adjacent said base to a second material structure adjacent said heterojunction, said first structure being resistant to said permeation. .Iaddend..Iadd. 20. An improved photovoltaic cell according to claim 19, wherein said first and second material structures each form distinct first and second sublayers, respectively, of said first layer. .Iaddend..Iadd. 21. An improved photovoltaic cell according to claims 19 or 20, wherein said first material structure includes a first crystallite size and said second material structure includes a second crystallite size. .Iaddend.