Copper Plating Contacts for Solar Cells: Replacing Silver with Copper

… more less Copper plating contacts are the main way to replace most of the silver on a solar cell. Copper conducts almost as well as silver and is far more common. But it cannot simply be printed and fired like silver paste. Copper atoms move fast through hot silicon and act as traps that kill carriers. So the factory first lays down a thin barrier, usually nickel. Then the cell sits in a plating bath of copper sulfate in dilute sulfuric acid. An electric current reduces copper ions to metal on the exposed lines: Cu2+ + 2e- -> Cu. A thin tin or silver cap keeps the copper from oxidising. To plate only the lines, the rest of the surface is masked or opened by laser. Plating has its own waste. The spent baths and rinse water carry dissolved copper, nickel and acid. Copper is toxic to fish and water life even at low levels. Treatment raises the pH so the metals drop out as solid hydroxides, which are pressed into sludge. Some plants recover the copper. There are other trade-offs too. Adhesion, long-term reliability and extra process steps have slowed its spread. A gentler path mixes copper into the paste, such as silver-coated copper powder. Each gram of silver saved also avoids mining waste far upstream. After this Concept you can explain why copper needs a barrier and judge the waste it trades for the silver it saves.