Electrolyte composition

Abstract

The electrolyte composition is used in a method of depositing metals, in particular, onto substrates, especially solar cells. The electrolyte composition is particularly suitable for the deposition of metals, in particular silver, onto solar cells. The electrolyte composition is preferably free of cyanides and contains at least one metal, preferably silver, and an iminodisuccinate derivative, preferably a sodium or postassium iminodisuccinate.

Description

CROSS-REFERENCE[0001]The subject matter described and claimed herein below is also described in German Patent Application No. 10 2009 029 558.5, filed on Sep. 17, 2009 in Germany. This German Patent Application provides the basis for a claim of priority of invention for the invention described and claimed herein below under 35 U.S.C. 119 (a)-(d).BACKGROUND OF THE INVENTION[0002]1. The Field of the Invention[0003]The present application relates to an electrolyte composition for the deposition of metals onto substrates. The electrolyte composition at least comprises the metal ions of the metal which should be deposited with this composition.[0004]2. The Description of the Related Art[0005]The galvanic deposition of metals from electrolyte solutions is known in the art. For this purpose the respective metal must be dissolved in the electrolyte solutions to form its ion and to maintain it in this state. For the latter purpose complexing agents are usually used. An important criterion fo...

AI Technical Summary

Benefits of technology

[0011]It is the object of the invention to provide an electrolyte composition which combines a high deposition rate with a high stability with respect to foreign ions and fluctuations of the pH and which at the same time does not have toxicity. In addition, the electrolyte composition should be suitable to be used for deposition of metals, in particular silver, onto solar cells.

[0015]In the above formula each of the R1, R2, R5 and R6 groups is selected from the group consisting of O, S and NH; each of the R3, R4, R7 and R8 groups is selected from the group consisting of OH, NH2, SH, O− and S−, and when at least one of the R3, R4, R7 and R8 groups is an O− or S− the IDSD is a salt comprising a sodium and / or potassium cation. The IDSD has the advantage of excellent complexing properties for numerous metals so that the composition according to the present invention is well suited for the deposition of a large number of metals. At the same time, the sensitivity of the electrolyte composition is decreased, since also impurities in the form of foreign ions can form complexes so that in the solution no precipitation takes place. In addition, IDSD is not toxic and is biodegradable. The IDSD of the present invention is preferably used in the form of its alkali metal salts. These are for example the sodium salt or the potassium salt, wherein the sodium salt is a preferred embodiment of the present invention. In particularly preferable embodiments the IDSD is an iminodisuccinate, in particular tetrasodium iminodisuccinate.

[0019]Under consideration of the above-mentioned amounts the IDSD can substantially increase the current efficiency of the deposition process.

[0021]In preferred embodiments the additional complexing agent can be used in the electrolyte composition in a concentration of 50 g / L to 250 g / L. More preferably the concentration is in a range from 100 g / L to 175 g / L. As already mentioned above, hydantoin cannot form complexes with many foreign ions. Here the term “foreign ions” means ions of nickel, chromium and iron. However, when hydantoin is used together with IDSD, an electrolyte solution with a very low sensitivity can be prepared. This combination of complexing agents has the additional advantage that higher amounts of the metal ion can be complexed. For example, the complexing agent IDSD alone can only complex up to 20 g / L of silver, but in combination with 5,5-dimethyl hydantoin up to 60 g / L can be complexed.

[0023]In preferred embodiments the electrolyte composition according to the present invention comprises a conductivity additive. The conductivity additive improves the conductivity of the electrolyte composition and thus reduces the cell voltage during the galvanization process. This is desirable, because with a better conductivity of the electrolyte solution an improved current efficiency can be achieved. According to the present invention, preferably the conductivity additive is a citrate. This citrate is preferably present in a concentration of 20 g / L to 75 g / L, more preferably 30 g / L to 50 g / L. In this case citrate has not only the function of a conductivity additive, but does also form complexes with calcium and magnesium ions. In addition, the use of citrate has the advantage that the electrolyte solution is not sensitive with respect to the incorporation of acids, since citrate can act as a buffer when fluctuations of pH occur. Therefore, this addition provides an advantage regarding the stability of the composition. A preferred citrate for use in the electrolyte composition of the invention is tripotassium citrate.

Problems solved by technology

However cyanide has the disadvantage of being extremely toxic so that its use as a complexing agent is not desired.

Therefore much effort has been made to replace the toxic complexing agent cyanide by other complexing agents.

Known electrolyte compositions free of cyanide have one crucial disadvantage, namely very low deposition rates of only 0.8 to 1 μm per minute.

Not only the acquisition and maintenance costs of the facility will be greatly increased, but also the cost of the electrolyte composition.

On the one hand, the galvanic deposition of silver onto solar cells is particularly desirable, because the applied layer has a conductivity which is near the theoretical conductivity, but on the other hand it is technically challenging.

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