Investigation of Metal Co-evaporated Copper Seed Layers for Copper-Plated 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. However, a plated copper contact on an indium-tin-oxide (ITO) generally has low a reliability of adhesion. For this reason, proper seed layer materials are required for adhesive copper plating. As a requirement for a suitable seed layer material, the contact resistance between the seed and the ITO is also important, as well as the adhesion, because high series resistance results in a low fill factor. In this research, we deposited a seed layer by co-evaporating copper with other metals (Cu-X). The contact resistivity ( ρ c ) of the Cu-X deposited on ITO was evaluated by using the transfer length method (TLM). In order to confirm the influence of the work function of the Cu-X, we measured the contact potential difference (CPD) by using photoemission in an air system (PAS). Moreover, phase and we analyzed the crystallite size by using X-ray diffraction (XRD) measurement.