Today, the solar industry accounts for about ten percent of the global silver consumption. To reduce the silver demand and the corresponding costs, researchers at the Fraunhofer Institute for Solar Energy Systems ISE are developing alternative materials and processes for solar cell metallization.
Industrial TOPCon solar cells with plated nickel/copper/silver metallized contacts achieved higher efficiency than their counterparts with printed silver contacts, and the silver consumption was reduced by over 90 percent in the process.
As part of two projects funded by the German Federal Ministry for Economic Affairs and Climate Action BMWK (formerly BMWi), a research team from Fraunhofer ISE used electroplating to metallize bifacial TOPCon solar cells with nickel/copper/silver contacts.
The aim was to replace silver solar cell contacts with copper, which is more readily available and about 100 times cheaper. Electroplated copper is compact and highly conductive.
The Freiburg researchers achieved a peak cell efficiency of 24 percent for the TOPCon cell with electroplated contacts. This efficiency is 0.5 percent higher than that of their industry partner’s reference cells, which were metallized using the silver screen-printing process.
Thanks to the substitution of printed silver by a stack of nickel/copper/silver, the silver consumption could be reduced by more than 90 percent for TOPCon solar cells.
This reduction was made possible by decreasing the width of the laser contact openings to a maximum of 5µm, among other factors. "In industrial production as well, the use of electroplating for metallization enables significant savings in silver without having to make any sacrifices in efficiency," says project manager Dr. Sven Kluska, assessing the project results.
In the project, the electroplating processes for metallization, developed at Fraunhofer ISE, were tested for industrial suitability on equipment from Rena Technologies GmbH. Both partners are continuing to work together in a follow-up project, carrying out process optimizations in order to further increase the efficiency and further develop the technology.
In addition to TOPCon solar cells, Fraunhofer ISE is also developing a copper electroplating process for the metallization of the equally promising silicon heterojunction (SHJ) solar cells. The Fraunhofer spin-off company, PV2+, is to transfer this process to industrial production.
