IL29043A - Process of coating substrates particularly for the manufacture of solar cells - Google Patents

Description

3 D UJ 1 ϋ Π 0 1 Π Ι D D p 1 Π 1 IMPROVEMENTS IN RELATING TO PROCESS OF COAT NO SUBSTRATES PARTICULARLY FOR THE MANUFACTURE Of SOLAR AMNON ISRAEL A D STATE OF PRIME OFFI nan The present invention concerns improvements in and relating to processes of coating The invention is particularly useful in the manufacture of solar or cells and is therefore described with respect to this Solar or cells are devices which convert particularly directly into One type as the active cadmium sulfide and copper with a layer of tin oxide as the negative current collector The layer is transparent in a In a cell the positive current collector layer is transparent or may be in the form of a Many techniques have been devised for applying the various for vacuum deposition and chemical precipitation both of which are quite The recent literature describes a process involving spraying a solution of two compounds onto the the latter being heated to induce the compounds to react to form the For see British Patent the article appearing in by Pergamon pages While the literature indicates that efficiencies as high as are obtainable by cells made in accordance with this in actual practice it has been found that this efficiency is obtainable by the process disclosed the heated substrate only in the case of very small and that the effiency in most cases involving cells made by this process is less than In in all cases the cost of manufacturing such cells as described in the literature is quite into widespread commercial use insofar as we are An of the present invention is to provide improvements in and relating to processes of coating More an object of the invention is to provide a process for applying copper sulfide coatings in the manufacture of solar cells so as to increase their even in the case of large and to reduce their cost of According to one feature of the invention there is provided a process of coating a substrate with copper sulfide characterised in spraying a mixture including a solution of a soluble copper salt dissolved in a volatile solvent and a solution of sulfur in elemental form dissolved in a volatile solvent onto the substrate while the latter is heated to a temperature which induces the copper salt and the elemental sulfur to form a coating of copper The solution of the soluble copper salt preferably includes a ammoniacal type Pyridine has been found to give particularly good but other ammoniacal type compounds could be for ammonia and their reduced The volatile solvent for the elemental sulfur is preferably and the ratio is preferably to In the embodiment described the substrate is supported on a holder whose temperature is maintained at during the spraying A plurality of thin films of the copper sulfide are applied to the substrate sprayin of a further plurality of thin The substrate is then transferred to a hot plate at about and baked for 45 seconds at this Insofar as we are aware this is the first time that the provided ingredient has the of elemental sulfur in this type of the provided producing ingredient has the form of a and thiolact c We have found that remarkably improved results are obtained when it is in form in this As indicated the above process applying a copper sulfide layer is particularly useful with respect to the production of solar cells including layers of tin cadmium and copper According to a further feature of the the tin oxide layer is applied by spraying a mixture including for the stannous chloride stannous formaldehyde and a solven a subslaate while the latter is heated to a temperature which induces the stannous chloride to react to the tin oxide According to a further important the invention provides a process coating a by spraying the for the ingredients in the mixture sustrate with a spraying mixture including a volatile solvent while the substrate is heated to a temperature which induces ingredients in the spraying mixture to react to form a thin either film on the substrate and while movin substrate or the spraying head with respect to the Other so as to a plurality of such In the described the substrate is supported on a holder which is rotated the s ra ing o the spraying head and the substrate so that the spraying mixture impinges on the substrate for onl a fraction of the rotational cycle of the For volume a plurality o the substrates would be arranged around the circumference of the holder so that the spraying mixture impinges on each in succession during the rotation of the It has been found that the foregoing features not only substantially reduce the cost of manufacture of the but that the deposit of each of the various layers as a plurality of very thin and uniform also substantially he properties of the cell so Further and advantages of the invention will be apparent from the description below wherein the invention described for purposes of example only with reference to the accompanying drawings and to examples set In the is a perspective view of a backwall solar cell made by the process of the present and is a schematic view of one form of apparatus that may be used in this With reference there is shown a of solar including a substrate or plate 2 glass or suitable a transparent current collector layer 4 of tin a layer 6 of cadmium a layer of copper sulfide and a layer conducting silver paint 10 serving as the second current The layers 6 and 8 are preferably applied by the use of the apparatus illustrated in It includes a rotatable annular table 12 heated by a heater A plurality x or x but could be of larger or smaller depending on the desired size of the finished solar The size here is not as limiting a factor as in prior since by the present method large size cells can be produced with relatively high as indicated A spraying head coupled to liquid reservoir 18 and air supply is disposed over the table in line with the plates 2 as the latter pass under the head during the rotation of the The plates 2 and the head 16 are thus eccentric to the axis of rotation of the the spraying mixture from head 16 impinging on each plate in succession during the rotation of the In this a thin and uniform film of the coating material is applied to each plate during each rotation of the table and it takes only a very short period of time to apply a large number of such The tin oxide layer 4 may be applied by one of the conventional methods of applying this such as the known vapour desposition either before using the apparatus illustrated in or by the use of such the tin oxide layer is applied by the use of the described apparatus with a spraying mixture constituted by including the 20 stannous chloride 80 hydrochloric acid 5 ammonium fluoride formaldehyde ethyl alcohol to make 1000 Table 12 is heated to a temperature between which induces the stannous chloride and the formaldehyde to react to produce a thin film of tin oxide during each rotation of the The ammonium fluoride appears to act as an produces higher transparency the film and clarity of the glass than hydrogen preferably having a boiling point between is used as the solvent in place of water to avoid cracking the Methyl alcohol could be but ethanol is A plurality of films are applied in this manner to n produce a layer of about 3μ having a conductivity of about ohms and having about visible is applied the cadmium sulphide layer A solution of cadmium thiocyanate dissolved in a mixed solvent containing methanol and ethanol a volume ratio of about may be used for applying this During the application of this the temperature of the rotatable table 12 is maintained by heater 14 at between preferably about The cadmium thiocyanate decomposes at this temperature and deposits a thin film of cadmium sulf de during each spray For a plate 2 of about x about preferably 22 of cadmium sulfide should be This takes about preferably about The copper sulfide layer 8 is then and as indicated this is effected by the use a solution containing sulfur in elemental form dissolved in a volatile In this the spray solution consists of copper acetate in pyridine in a solution of sulfur in The crystalline sulfur is obtained by dissolving supplied oxt ing the commercially sulfur in benzene which separates the amorphous from the crystalline The sulfur per atom of eupric Ethyl alcohol is added to dilute the and the mixture is allowed to age for at least one during which time it may be heated to reflux in order tomaintain the crystalline sulfur in Particularl good results have been obtained when the mixture the copper sulfide layer 8 is applied in the following The rotatable table 12 is heated to a temperature of and 10 of the mixture are sprayed onto the plates The temperature is then raised to about for about four whereupon it is found that the yellowish layer resulting from the deposit turns the composition having been converted to copper About more films are then applied at this producing only green The plate is then removed to a hot plate previously heated to and is baked for 45 seconds under these The green colour is observed to movin from the centre to a brown colour Upon it was found that the green colour is due to cupric and that the brown colour is due to cuprous In making type of solar the plate is masked around the edges between the application of the cadmium sulphide and the copper sulphide This mask is removed before the baking step After the baking the cadmium sulphide layer beneath the mask not exposing covered by copper sulfide is the tin oxide Nickel is electroplated at the edges for soldering the cell is then and the long edges are coated with silver The entire cell is baked at for 45 encapsulating when in this dry condition to prevent SS the of She spraying mixture applying the copper sulphide layer in the above described procedure was of the following Example Solution cupric 200 pyridine 800 cc ethanol Solution yellow 1 litre benzene Per lOOcc of there is mixed 260cc of Solution The ratio is about Followin is another example of a sprayin mixture which may be used applying the copper sulfide layer Example Solution cupric formate 50cc 50cc ethanol Solution Solution of sulphur in Per lcc of is mixed of solution The ratio is about The cells produced by the use of the solutions of Examples 1 and 2 in the procedure were tested in a The photovoltaic current which was generated when the monochromator light fell on the copper sulfide layer was collected and recorded on a low resistance The continuous light emitted from a tungsten ribbon band was filtered with heat absorbing optical filters before entering the When the wavelength of the incident light was the current intensity exhibiting two pronounced peaks for each at For comparison following are the results of the two cells in arbitrary for and the ratio of In Example Ig In Example Ig and The voltage in the sun for both cells was about These two cells which the sulfur was in elemental form dissolved in the solvent as described were compared with cell produced from a known coating mixture in which the sulfur was in the form of a namely For the latter the mixture was made as Solution At 23cc ethanol 27cc ethanol Solution Thiorea in ethanol The solutions were cooled in ice and mixed immediately before 5cc of solution A having been mixed with 12cc of solution B and kept in ice with ammonium When this mixture was used for applying the copper sulfide the remainder of the procedure being the the tests with the gave the following lg 58 and It is thus seen that the results produced by Examples 1 and wherein the sulfur was in elemental form in the spraying far exceeded the results produced in the described test wherein the sulfur was in the form of a compound In the mixture in the test was very unstable at room temperature and had to be kept in whereas the stability of the solutions in Examples was indefinite for Example Solution cupric lOcc Benzene to make Solution of solution of sulfur in Per lcc of solution A there is mixed 2ec of solution The sulfide ratio is about While benzene is preferred as the volatile solvent for the elemental other such solvents may be for example toluene and The present invention enables the production of solar cells at a far cost than heretofore estimated at one order of magnitude below the present cost of solar the invention enables the production of solar cells having efficiencies as contrasted with about the maximum efficiency heretofore obtainable in solar indicated efficiencies of up to were heretofore obtainable apparently only in the case of cells or in large cells produced by expensive vacuum deposition In the present invention enables the production of solar cells which are uniformly reliable even when produced on a volume Many variations and applications of the illustrated embodiments may of course be insufficientOCRQuality

Claims (22)

1. HAVING NOW particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:- 1. A process of coating a substrate with copper sulfide characterised in spraying a mixture including a solution of a soluble copper salt dissolved in a volatile solvent and a solution of sulfur in elemental, form dissolved in a volatile solvent onto the substrate while the latter is heated to a temperature which induces the copper salt and the elemental sulfur to react to form a coating of copper sulfide.

2. A process according to Claim 1, wherein the solution of the soluble copper salt includes an ammoniacal type compound.

3. A process according to Claim 2, wherein saidaamoniacal compound is pyridine.

4. A process according to any one of Claims 1-3, wherein the soluble copper salt is cupric-acetate.

5. A process according to any one of Claims 1-3» wherein the soluble copper salt is cupric formate.

6. A process according to any one of Claims 1-3, wherein the soluble copper salt is cupric-acetyl-acetate,

7. A process according to any one of Claims 1-6, wherein the volatile solvent for the elemental sulfur is benzene.

8. A process according to any one of Claims 1-6, wherein the volatile solvent for the elemental sulfur is cyclohexane, toluene or trichloroethylene.

9. A process according to any one of Claims 1-8, wherein the copper-to-sulphur ratio is 1:10 to 1:40.

10. A process according to any one of Claims 1-9, wherein the substrate is supported on a holder whose temperature is 145-150°C, during the spraying operation.

11. thin films are sprayed onto the substrate while the holder is at a temperature 145-15Q°C, the temperature of the holder is then raised to 165-170°C, and a further plurality of thin films are then sprayed on top of the first-mentioned films.

12. · A process according to Claim H wherein the copper-sulfide-coated substrate is heated on a hot-plate preheated to a temperature of 360°C, following the last spraying operation.

13. A process accordin to any one of Claims 1-12 wherein the substrate is supported on a holder which is rotated during the spraying operation, the spraying head and the substrate both being eccentric to the axis of rotation of the holder so that the spraying mixture impinges on the substrate for only a fraction of the rotational cycle of the holder.

14. A process according to Claim 13* wherein a plurality of substrates Tbatanooo are arranged in a circle around said holder so that the spraying mixture impinges on each in succession during the rotation of the holder.

15. A process for producing a solar cell comprising applying to a non-conductive substrate, layers of tin oxide, cadmium sulfide and copper culfide, characterised in that the copper sulfide layer is applied in accordance with the- method of any one of Claims 1-14.

16. A process for producing a solar cell according to Claim 15 , wherein the tin oxide layer is applied by spraying a mixture including stannous chloride, formaldehyde, and a for the stannous chloride, solvent/ onto the substrate while the latter is heated to a temperature which induces the stannous chloride and formaldehyde to react to form the tin oxide layer.

17. A process according to Claim 16, wherein said stannous chloride spraying mixture includes ammonium fluoride.

18. said solvent is alcohol having a boiling point of 60-80 C,

19. A coated substrate when ever produced in accordance with the process of any one of Claims 1-14.

20. A photovoltaic cell whenever produced in accordance with the process of any one of Claims 15-18.

21. A process of coating a substrate with copper sulfide substantially as described with reference to any of the disclosed examples.

22. A process of producing a solar cell substantially as described with reference to any ofie of the disclosed examples. COHEN ZEDEK & SPISBACH P.O. Box 33116, Tel Aviv Attorneys for Applicants