Characterizations of Cu/Sn-Zn Solder/Ag Interfaces on Photovoltaic Ribbon for Silicon Solar Cells

Sn-xZn (x = 9, 25, and 50 wt%) alloy solders are applied in photovoltaic (PV) ribbon and connected with silicon solar cells. The interfacial microstructures, series resistance, and bonding strength of Sn-xZn PV modules are investigated. Cu5Zn8 and AgZn3 intermetallic compounds (IMCs) were found at the interfaces. The Zn content in the solder dominates the growth behavior of IMCs at the interface. The thickness of the Cu5Zn8 and AgZn3 IMC layer increased with increasing Zn content in the solder, and thus, the series resistance of the PV module also increased. The growth of IMCs can enhance the interfacial adhesion strength, but excess Zn overconsumes the Ag electrode, reducing the bond strength of the PV module. Applying low-Zn-content Sn-xZn solder to PV ribbon avoids overconsumption of the Ag layer and, thus, decreases the series resistance and internal stress.