30% Silver Reduction in Rear Bus Bar Metal Paste

With decreasing module prices on the spot market, the cost of silver is getting more and more important in solar cell fabrication. Silver is necessary for the front side metallization and the rear side bus bar metallization in a solar cell. The front side benefits from the good conductivity of silver whereas the rear side bus bars need the low oxidation degree and thus the good solderability of this noble metal. We replace silver bus bars by a metal paste containing a combination of different metals with a silver content below 40%. Thus we reach a silver reduction of 30% compared to conventional rear bus bar metal paste. Multi crystalline silicon solar cells with the new paste achieve identical efficiencies compared to cells with silver reference pastes, tested on 150 cells per batch. The new paste simply replaces conventional rear bus bar metal pastes and passes the common tests. Reliability tests are in progress at the moment. As a pretest, cells with the paste passed a hot-water test. Losses in efficiency of the cells due to corrosion are comparable to the losses of cells with reference silver paste.