Study of Cu-X alloy seed layer on ITO for copper-plated silicon heterojunction solar cells

For the reduction of optical loss and contact material cost in silicon heterojunction (SHJ) solar cells, copper plating has been considered as a suitable metallization technique. Usually, a metal seed layer is deposited on an indium tin oxide (ITO) prior to copper plating for adhesive contact between copper and ITO. As a requirement of suitable seed layer material, contact resistivity (ρc) between the seed and the ITO is also important, as well as the adhesion, because high series resistance results in fill factor loss. In this study, we applied alloy seed layers which were deposited by co-evaporating copper with other metals (Cu-X). Contact resistivity values of the samples were extracted by using transfer length method (TLM). Also, tape tests were carried out to simply confirm the adhesion of contacts with different seed layers. Among the Cu-X alloy seed materials, the Cu-Ni alloy film resulted in good adhesion to the ITO as well as low average contact resistivity under 1 mΩ cm2.