Microstructural surface analysis of Ni/Cu front contact after peel force test to improve contact adhesion

Abstract

ABSTRACTNi/Cu two-step plating has been applied to solar cells as a metallization technique since it has low contact resistance after nickel sintering process, and is suitable for fabricating narrow fingers. However, a reliable adhesion of the Ni/Cu contact is still one of the remaining challenges. In this experiment, a peel force test was used to investigate the dependence of varied sintering temperatures on the adhesion of the Ni/Cu front contact. The surface of the bus bars was observed by field emission scanning electron microscope (FE-SEM) to analyse the high and low adhesion regions. When the adhesion result was high, silicon chunks from the substrate were often observed on the nickel layer (ribbon side). Also, the influence of oxidation on the nickel surface during sintering was discussed with the oxygen atomic ratio, which was measured by energy dispersive spectroscopy (EDS). Decent adhesion values up to 1.16 N/mm average with 2.47 N/mm maximum have been achieved with good soldering process.