Image: PV2+

Cop­per instead of sil­ver: new boost for solar cell production

Ris­ing raw mate­r­i­al prices and a lack of avail­abil­i­ty, espe­cial­ly of sil­ver, are caus­ing the pro­duc­tion costs of pho­to­volta­ic mod­ules to rise. Researchers at the Fraun­hofer Insti­tute have devel­oped an elec­tro­plat­ing process in which the expen­sive pre­cious met­al sil­ver is sub­sti­tut­ed by read­i­ly avail­able cop­per. The researchers were able to replace the poly­mers that are usu­al­ly pro­duced dur­ing elec­tro­plat­ing, which are cost­ly to dis­pose of. Instead, they use alu­minum for mask­ing, which can be eas­i­ly recy­cled. In order to bring the tech­nol­o­gy to mar­ket more quick­ly, the spin-off PV2+ was founded.

 

Pho­to­voltaics is a main­stay of elec­tric­i­ty gen­er­a­tion from renew­able ener­gies. Mod­ern het­ero­junc­tion solar cells have a par­tic­u­lar­ly lowcar­bon foot­print due to their low sil­i­con con­sump­tion and achieve the high­est effi­cien­cies in indus­tri­al pro­duc­tion. Accord­ing­ly, there is a good chance that this tech­nol­o­gy will become the stan­dard in pro­duc­tion. The fig­ures prove the increas­ing impor­tance of pho­to­voltaics. Accord­ing to the Inter­na­tion­al Renew­able Ener­gy Agency (IRENA), glob­al elec­tric­i­ty gen­er­a­tion from pho­to­volta­ic sys­tems was more than 96 TWh in 2012, ris­ing to near­ly 831 TWh by 2020. Accord­ing to the Fed­er­al Envi­ron­ment Agency, elec­tric­i­ty gen­er­a­tion from pho­to­voltaics in Ger­many rose from just under 27 TWh to just under 50 TWh in the same period.

The poten­tial of pho­to­voltaics is far from exhaust­ed. How­ev­er, valu­able sil­ver is used in the man­u­fac­ture of solar cells for the con­duc­tive tracks and con­tacts. They dis­si­pate the cur­rent gen­er­at­ed in the sil­i­con lay­er by solar radi­a­tion. Prices for the pre­cious met­al are ris­ing; sil­ver already accounts for around 10 per­cent of the man­u­fac­tur­ing price of a pho­to­volta­ic cell. Fur­ther­more, sil­ver is only avail­able in lim­it­ed quan­ti­ties on earth. The solar indus­try process­es 15 per­cent of the sil­ver mined. Due to the strong growth, this share would have to rise sharply. How­ev­er, this is hard­ly fea­si­ble, as oth­er indus­tries such as elec­tro­mo­bil­i­ty or 5G tech­nol­o­gy are also announc­ing high­er sil­ver con­sump­tion for the future. There­fore, the solar indus­try will not be able to real­ize its full pow­er with­out break­through tech­no­log­i­cal innovations.

Cop­per for the conductors

Researchers at the Fraun­hofer Insti­tute for Solar Ener­gy Sys­tems ISE have tak­en up this chal­lenge. With around 1400 employ­ees, the Fraun­hofer Insti­tute in Freiburg is the largest solar research insti­tute in Europe. A team of researchers led by Dr. Markus Glatthaar, an expert in met­al­liza­tion and pat­tern­ing, has devel­oped an elec­tro­plat­ing process that replaces sil­ver with cop­per in the promis­ing het­ero­junc­tion tech­nol­o­gy. Cop­per is many times cheap­er and more read­i­ly available.

To pre­vent the entire elec­tri­cal­ly con­duc­tive sur­face of the solar cell from being elec­tro­plat­ed with cop­per, the areas that are not to be coat­ed must be masked before­hand. These areas receive an elec­tri­cal­ly insu­lat­ing coat­ing that pre­vents gal­van­ic depo­si­tion. Thus, the cop­per lay­er grows only in the non-insu­lat­ing coat­ed areas.

The researchers have made a sec­ond sig­nif­i­cant advance here: To mask the sil­i­con wafer in the elec­trolyte bath, the indus­try pre­vi­ous­ly used expen­sive poly­mer-based coat­ings or films. Prop­er dis­pos­al of the poly­mers is cost­ly and caus­es a lot of waste. Glatthaar and his team suc­ceed­ed in sub­sti­tut­ing the poly­mers with alu­minum. Like cop­per, alu­minum can be ful­ly recy­cled. The dou­ble switch — from sil­ver to cop­per and from poly­mer to alu­minum — also brings a dou­ble advan­tage: the pro­duc­tion of solar cells becomes more sus­tain­able and at the same time sig­nif­i­cant­ly cheaper.

Break­through with inno­v­a­tive elec­tro­plat­ing and improved electrolyte

How did the researchers man­age to replace the expen­sive pre­cious met­al sil­ver? “We have devel­oped a spe­cial elec­tro­plat­ing process that makes it pos­si­ble to use cop­per for the con­duc­tive tracks instead of sil­ver,” explains Glatthaar. Even the per­for­mance is improved as a result. This is because the cop­per con­duc­tors are par­tic­u­lar­ly nar­row thanks to laser struc­tur­ing. Due to the extreme­ly small diam­e­ter of only 19 microm­e­ters, the shad­ow­ing of the light-receiv­ing sil­i­con lay­er is less than with sil­ver tracks. This improves the per­for­mance and ulti­mate­ly the elec­tric­i­ty yield.

The sec­ond tech­no­log­i­cal achieve­ment of the Fraun­hofer team is the use of alu­minum as a mask­ing lay­er. One dif­fi­cul­ty is that alu­minum is elec­tri­cal­ly con­duc­tive and there­fore not suit­able for mask­ing. The Fraun­hofer researchers take advan­tage of the fact that alu­minum forms an insu­lat­ing oxide lay­er on its sur­face by itself. But this is only a few nanome­ters thick. “We suc­ceed­ed in adapt­ing the process para­me­ters and devel­op­ing a spe­cial elec­trolyte so that the extreme­ly thin, native oxide lay­er of the alu­minum can reli­ably ful­fill its insu­lat­ing func­tion. This was an impor­tant mile­stone for the suc­cess of our research project,” says Glatthaar.

The recy­clable mate­ri­als cop­per and alu­minum bring pho­to­volta­ic pro­duc­tion one step clos­er to the cir­cu­lar econ­o­my. This also improves envi­ron­men­tal and social stan­dards. “Since we have enough cop­per in Ger­many, the sup­ply chains are short­er, and depen­dence on the price on the inter­na­tion­al raw mate­r­i­al mar­kets or on for­eign sup­pli­ers is reduced,” adds Glatthaar.

Spin-off PV2+ brings solar tech­nol­o­gy to market

In order to bring this promis­ing tech­nol­o­gy to mar­ket more quick­ly, Fraun­hofer ISE has found­ed the spin-off PV2+. The let­ters P and V stand for pho­to­voltaics, 2+ for two pos­i­tive­ly charged cop­per ions in the elec­tro­plat­ing bath. The com­pa­ny is also based in Freiburg. Fraun­hofer researcher Markus Glatthaar serves as CEO of the spin-off. He wants to set up pilot pro­duc­tion togeth­er with indus­tri­al part­ners as ear­ly as the begin­ning of 2023.

Prof. Dr. Andreas Bett, Insti­tute Direc­tor at Fraun­hofer ISE, explains: “The inno­v­a­tive solar cells are an impor­tant build­ing block for the future pow­er sup­ply from renew­able ener­gies and will give the pho­to­volta­ic indus­try a much need­ed boost. The spin-off has the best chances to estab­lish itself quick­ly and suc­cess­ful­ly on the mar­ket. Of course, we are all the more pleased that these tech­nolo­gies were cre­at­ed at our insti­tute.” In addi­tion, the Ger­man Fed­er­al Min­istry of Eco­nom­ics and Cli­mate Pro­tec­tion (BMWK) is fund­ing the project as part of its “Exist” start-up program.