Method of coating a glass ribbon on a liquid float bath

Abstract

A method of making low cost solar cells on a large scale basis by means of a continuous process of fabricating float glass and coating the float glass, in sequence, with tin oxide, cadmium sulphide, and copper sulphide, while the glass floats atop tanks of molten material in a furnace of proper temperature for each step of the process, the application of the coatings, in a preferred embodiment, being accomplished by depositing materials which form the coatings on contact with heated surfaces at such slow rates and, in the case of spray application, via drops of such uniformity that the float glass may (1) remain at uniform temperatures by virtue of the superior thermal conductivity of the molten material and retain those temperatures despite the abstraction of heat from the glass by evaporation of liquids and/or formation of crystalline layers, and (2) be substantially free of temperature gradients along the surface of the sheet glass.

What is claimed: 
     
       1. A method of fabricating large scale solar cells, comprising moving a continuous strip of glass continuously in a path containing sequential heated liquid float tanks, and forming a SnO x  film on said continuous strip of glass during traverse of said strip of a first of said float tanks, forming a film of CdS microcrystals on said SnO x  film during traverse of said strip through a second of said float tanks, and forming a film of Cu 2  S over said CdS film during traverse of said strip through a third of said float tanks, wherein said float tanks contain liquid at temperatures suitable for formation of said films, and wherein said films are spray deposited at rates selected to enable said liquid in said float tanks to maintain the temperatures of the surfaces of said strip of glass constant during the forming of said films. 
     
     
       2. The combination according to claim 1, wherein said forming of said films is accomplished by spraying of solutions onto said strip, said solutions containing compounds selected to interact to form said films in the presence of heat, and said strip being maintained free of temperature gradients along the surface of the strip at the sprayed areas. 
     
     
       3. The combination according to claim 1, wherein said forming of said SnO x  film is accomplished by spraying on said strip, while said liquid metal is maintained at 950° F. an atomized solution in the proportions of 500 cc methanol, 140 gm SnCl 2  (anhydrous), 1.4 gm phenylhydrozene hydrochloride, and 6.0 gm .[.ammonium bisulphide.]. .Iadd.ammonium bifluoride .Iaddend.to a thickness of about 0.4 microns. 
     
     
       4. The combination according to claim 1, wherein said forming of said SnO x  film is accomplished by spraying a methanol solution of SnCl 2  .[.in air.]. as uniform atomized droplets against said continuously moving strip of glass while said strip is maintained without macroscopic temperature gradients along the surface of the strip at about 950° F. 
     
     
       5. The combination according to claim 4, wherein said CdS film of microcrystals is formed by depositing an atomized spray on said film of SnO x , said atomized spray solution having the proportion of 5 liters of deionized water, 75 cc 1 Molar .[.N N dimethylthiourea.]. .Iadd.thiourea .Iaddend.solution, 100 cc 1 Molar CdCl 2  .21/2 H 2  O solution, 0.3 gm AlCl 3  .6H 2  O at a temperature of 620° F. while maintaining said strip and said film of SnO x  free of macroscopic temperature gradients along the surface of the strip, said CdS film being about 1 to 2 microns thick. 
     
     
       6. The method according to claim 1, wherein said strip is .[.created.]. .Iadd.coated .Iaddend.with an acid spray prior to coating of said SnO x  film, said acid spray including H 2  SiF 6 , and the surface of said strip during said spray being at about 950° F. 
     
     
       7. A method of fabricating large scale photovoltaic cells, comprising floating a continuous strip of glass in a path containing sequential liquid float tanks, forming a SnO x  film on said continuous strip of glass during traverse of said strip of a first of said float tanks, forming a film of CdS microcrystals on said SnO x  film during traverse of said strip through a second of said float tanks, wherein said float tanks contain said liquid at temperatures suitable for formation of said films, and wherein said films are spray deposited at rates selected to enable said liquid in said float tanks to resupply sufficient heat to said glass to maintain the temperatures of the surface of said strip of glass constant during the forming of said films despite the cooling effect of said spray, and forming a film of Cu 2  S over said film of CdS microcrystals. 
     
     
       8. The method according to claim 7, wherein said forming of said films of SnO x  and CdS is accomplished by spraying solutions onto said strip, said solutions containing compounds selected to interact to form said films. 
     
     
       9. The method according to claim 8, wherein said forming of said SnO x  film is accomplished by intermittently spraying on said strip an atomized solution in methanol including SnCl 2  (anhydrous) and a fluorine salt, the intermittent spraying being at intervals sufficiently long to enable exposed surfaces of said glass to re-attain the temperature of the first of said float tanks despite cooling produced by said spraying. 
     
     
       10. The method according to claim 7, wherein said forming of said SnO x  film is accomplished by spraying intermittently in air a methanol solution including SnCl 2  as atomized droplets against said strip with sufficient times between sprays to enable the temperature of the upper surface of said strip to be at constant temperature during said spraying. 
     
     
       11. The method according to claim 7, wherein said CdS film of microcrystals is formed by depositing an atomized spray on said film of SnO x , said atomized spray including a water solution of .[.NN-DMthiourea.]. .Iadd.thiourea.Iaddend., CdCl 2 , and AlCl 3 . 
     
     
       12. The method according to claim 9, wherein said CdS film of microcrystals is formed by intermittently depositing atomized spray on said film of SnO x , said atomized spray including a water solution of .[.NN-DMthiourea.]. .Iadd.thiourea.Iaddend., CdCl 2 , and AlCl 3 . 
     
     
       13. The method according to claim 10, wherein said CdS film of microcrystals is formed by depositing atomized spray on said film of SnO x  in intermittent sprays, said atomized spray including a water solution of .[.NN-DMthiourea.]. .Iadd.thiourea.Iaddend., CdCl 2 , and AlCl 3 .