High Speed Copper Plating Process
A copper electrolyte comprising a copper nitrate salt is described. The electrolyte is suitable for use in a light induced plating process for metallizing contacts in a photovoltaic solar cell. A method of metallizing an electrical contact in a photovoltaic solar cell using the copper electrolyte is also described.
1 . A method of plating an electrical contact on a semiconductor solar cell substrate, wherein a first surface of the semiconductor solar cell substrate is covered with an anti-reflection coating and a second surface of the semiconductor solar cell substrate comprises a back electrode, wherein a grid pattern is formed in the anti-reflection coating comprising portions with the anti-reflection coating and portions without the anti-reflection coating, and a barrier metal is deposited on the grid pattern formed in the anti-reflection coating on the portions without anti-reflection coating either directly on the semiconductor solar cell substrate or on a silver paste, wherein copper metal is plated on the barrier metal by a process comprising the steps of:
a) immersing the semiconductor solar cell substrate in an electrolyte comprising a copper nitrate salt and wherein an anode is also immersed with the electrolyte;
b) causing the barrier metal to become cathodic by (i) exposing the first surface of the semiconductor solar cell substrate to electromagnetic radiation to generate a photovoltaic response and cause the semiconductor solar cell substrate to generate current in the electrolyte and/or (ii) applying an external current;
wherein copper metal is plated on the barrier metal;
and wherein the grid pattern is formed by either 0) directly removing portions of the anti-reflection coating, or by (ii) printing the silver paste in the image of the grid pattern on the anti-reflection coating and heating the semiconductor solar cell substrate to cause the silver paste to penetrate the anti-reflection coating.
2 . The method according to claim 1 , wherein the copper nitrate salt is anhydrous copper nitrate, a hydrated copper nitrate, or combinations of one or more of the forgoing.
3 . The method according to claim 1 , wherein the copper nitrate salt is copper nitrate hemi(pentahydrate).
4 . The method according to claim 1 , wherein the concentration of copper in the electrolyte is between about 10 g/L and about 150 g/L.
5 . The method according to claim 1 , wherein the electrolyte further comprises potassium nitrate or sodium nitrate.
6 . The method according to claim 5 , wherein the concentration of potassium nitrate or sodium nitrate in the electrolyte is between about 100 g/L and about 150 g/L.
7 . The method according to claim 1 , wherein the electrolyte further comprising a source of chloride ions.
8 . The method according to claim 1 , wherein the electrolyte comprises one or more additives selected from the group consisting of buffering agents, brighteners, wetters, wetting agents, suppressors, accelerators, cuprous ligands, and combinations thereof.
9 . The method according to claim 1 , wherein the pH of the electrolyte is between about 1 and 4.
10 . The method according to claim 1 , wherein the electrolyte does not contain any free sulfuric acid.
11 . The method according to claim 1 , comprising the step of depositing a final finish of (i) a metal more noble than copper or (ii) tin over the copper.
12 . The method according to claim 1 , wherein the barrier metal is selected from the group consisting of nickel, cobalt, palladium, tungsten, molybdenum, rhenium, chromium, platinum and alloys of any of the foregoing with phosphorus or boron.
13 . The method according to claim 1 , wherein the barrier metal is deposited by a light induced plating process.
14 . The method according to claim 1 , wherein the electrolyte is maintained at a temperature of between about 25° C. and about 35° C.