Reduction of Silver Use in Low-Temperature Interconnection of Solar Cells

New solar cells’ technologies such as silicon heterojunction and tandem solar cells raise new challenges such as temperature-induced degradations, which are problematic for the cells’ interconnection. Electrically Conductive Adhesives (ECAs), usually made of silver particles embedded in a polymeric matrix, seem a promising technology to allow low-temperature interconnection, but raise concern about a high consumption of silver in the manufacture of photovoltaic (PV) panels. In this work, the fabrication of copper-based ECAs is presented as an approach to reduce the silver consumption of the interconnection process. Core-shell copper-silver particles with dendritic shapes that showed resistant to oxidation up to 220°C were used as conductive fillers. Their integration into an acrylate fast-curing matrix was performed in ratios of 59 wt% and 69 wt% fillers, respectively accounting for silver contents of 3.0 wt% and 3.5 wt%. The resulting pastes have resistivities of 3.5 * 10‑3 Ω*cm and 9.0 * 10-4 Ω*cm respectively, globally similar to those of commercial ECAs dedicated to the interconnection of solar cells. Their fast-curing process was measured to occur upon heating at 105°C, and be completed upon heating at 160°C during 20 seconds, enabling high throughputs. First trials of these ECAs into strings of solar cells were made: the stencil-printed patterns had a good quality, but a poor adhesion between the solidified ECAs and the ribbons prevents their further use.