Photovoltaic cell

Abstract

A large area photovoltaic cell comprising a layer of multicrystalline cadmium sulfide, about 1 to 2 microns thick, formed by simultaneously spraying two suitably selected compounds on a uniformly heated plate of Nesa glass, thereafter forming a coating of Cu 2 S by spraying two suitable compounds over the cadmium sulfide layer while the latter is heated, to form a photovoltaic heterojunction, applying thereover a layer of CuSO4, and applying electrodes of Cu and Zn, respectively, to separated areas of the layer of CuSO 4 , and heating the cell to form a cuprous oxide rectifying junction under the copper electrode by reaction of the Cu electrode with the CuSO 4 , while diffusing the zinc through the body of the cell. The diffusion of the zinc provides a negative electrode coplanar with the positive copper electrode, eliminating any need for introducing mechanically complex provision for making a connection to the Nesa glass, while the use of a rectifying positive electrode enables use of a layer of CdS only 1 to 2 microns thick, rather than the usual 20 microns, despite the fact that such thin layers tend to have pinholes, which in the prior art render the cells inoperative but in the present teaching do not.

What is claimed is: 
     
       1. A solar cell, comprising a transparent conductive base, a layer of CdS microcrystals about 1 micron to 2 microns in thickness coated on said base, a layer of Cu 2  S coated over said layer of CdS microcrystals and forming a photovoltaic heterojunction therewith, a copper electrode superposed over a portion of said layer of Cu 2  S, a zinc electrode superposed over .[.a.].  .Iadd.another .Iaddend.portion of said layer of Cu 2  S, and a quantity of zinc diffused under said zinc electrode to provide a conductive path from said zinc electrode to said conductive base. 
     
     
       2. The combination according to claim 1, wherein .Iadd.there .Iaddend.is provided a layer of copper sulphate between said electrodes and said layer of Cu 2  S. 
     
     
       3. The combination according to claim 1, wherein .Iadd.there .Iaddend.is provided a rectifying Cu-Cu 2  O junction under said copper electrode, said junction being conductive in the direction out of said copper electrode. 
     
     
       4. The combination according to claim 1, wherein said electrodes are coplanar and interdigitated. 
     
     
       5. In a precursor photovoltaic cell, a conductive base, superposed layers of microcrystals on said conductive base, said superposed layers of microcrystals constituting a photovoltaic heterojunction, and a rectifying junction output electrode overlying said superposed layers of microcrystals, said rectifying junction being non-conductive in a sense such as to prevent flow of reverse current from said electrode into said heterojunction, said superposed layers of microcrystals including a layer of cadmium sulphide microcrystals and a layer of cuprous sulphide, said layer of cadmium sulphide microcrystals .Iadd.contacting said conductive base and .Iaddend.being about 1 to 2 microns thick, said rectifying junction is a copper - cuprous oxide layer, and a layer of .[.cuprous.]. .Iadd.curpic .Iaddend.sulphate being interposed between said electrode and said heterojunction. 
     
     
       6. A precursor photovoltaic cell, comprising a transparent conductive substrate, a first layer of photovoltaically active microcrystals on said substrate, a layer of microcrystals coated over said first layer and forming with said first layer a photovoltaic heterojunction, an electrode coating said heterojunction, said electrode being a rectifying coating non-conductive in the sense from said electrode to said conductive substrate, said photovoltaic heterojunction being constituted essentially of cadmium sulphide microcrystals as one layer and of cuprous sulphide as the other layer, wherein said cadmium sulphide layer .Iadd.contacts said substrate and .Iaddend.is about 1 or 2 microns thick, said rectifying coating being a cuprous oxide - copper rectifier, and a layer of .[.cuprous.]. .Iadd.cupric .Iaddend.sulphate interposed between said rectifying coating and said heterojunction. 
     
     
       7. In a precursor photovoltaic cell, a microcrystalline photovoltaic heterojunction, a layer of .[.cuprous.]. .Iadd.cupric .Iaddend.sulphate superposed over said heterojunction, a layer of copper superposed over said layer of .[.cuprous.]. .Iadd.cupric .Iaddend.sulphate, and copper oxide formed at the junction of said layers of .[.cuprous.]. .Iadd.cupric .Iaddend.sulphate and copper by interaction between said .[.cuprous.]. .Iadd.curpic.Iaddend.sulphate and said copper. .Iadd. 8. A solar cell, comprising a transparent conductive base,   a layer of CdS microcrystals coated on said base,   a layer of Cu 2  S coated over said layer of CdS microcrystals and forming a photovoltaic heterojunction therewith,   a metallic positive electrode superposed over a portion of said layer of Cu 2  S,   a zinc negative electrode superposed over another portion of said layer of Cu 2  S, and   a quantity of zinc diffused under said zinc electrode to provide a conductive path from said zinc electrode to said conductive base. .Iadd. 9. The solar cell described in claim 8, wherein said layer of CdS microcrystals is less than 20 microns in thickness. .Iadd. 10. The solar cell described in claim 9, wherein said positive electrode and said negative electrode are co-planar. .Iadd. 11. The solar cell described in claim 10, further including a rectifying junction layer interposed between said layer of Cu 2  S and said positive electrode. .Iadd. 12. The solar cell described in claim 11, wherein said rectifying junction layer includes Cu 2  O interposed between said CU 2  S layer and said positive electrode.