Abstract
This present study applied Cu∙Zn/Al ribbon in place of a traditional Cu ribbon to a photovoltaic (PV) ribbon. A hot-dipped and an electroplated Sn PV ribbon reflowed onto an Ag electrode on a Si solar cell and estimated the feasibility of the tested module (Ag/Solder/Cu∙Zn/Al). After bias-aging, a bias-induced thermal diffusion and an electromigration promoted the growth of intermetallic compounds (IMCs) (Cu6Sn5, Ag3Sn). To simulate a photo-generated current in the series connection of solar cells, an electron with Ag-direction (electron flows from Ag to Al) and Al-direction (electron flows from Al to Ag) was passed through the Al/Zn∙Cu/Solder/Ag structure to clarify the growth mechanism of IMCs. An increase in resistance of the Ag-direction-biased module was higher than that of the Al-direction biased one due to the intense growth of Cu6Sn5 and Ag3Sn IMCs. The coated solder of the electroplated PV ribbon was less than that of the hot-dipped one, and thus decreased the growth reaction of IMCs and the cost of PV ribbon.
Highlights
Photovoltaic (PV) ribbon structure is made of a Cu ribbon coated with an alloy solder
Note that the Cu layer does not exist in the HD PV
The Cu6 Sn5 intermetallic compounds (IMCs) grows at the Cu/Sn interface and the Ag3 Sn IMC combines the PV Al-ribbon and Si solar substrate (Figure 2a)
Summary
Photovoltaic (PV) ribbon structure is made of a Cu ribbon coated with an alloy solder. Low-cost Sn–Cu alloys are served as a candidate solder to substitute for Sn–Pb solder due to their good weldability with Cu [4,5]. IMC is not formed in the Sn–Zn alloy structure, which has good conductivity [8]. A previous study reported that adding more Zn to the Sn-xZn solder could reduce the resistivity and the cost of the solder [9]. Highly active Zn is oxidized to form scum in the molten Sn–Zn alloy, decreasing solder weldability. Using a protective atmosphere or a flux during soldering, or adding appropriate alloying elements (Al, Cr, In) to a solder can improve the weldability between the solder and a Cu ribbon [10,11]
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