Contact resistivity and adhesion of copper alloy seed layer for copper-plated silicon heterojunction solar cells

Abstract

To reduce 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 indium tin oxide (ITO) generally has low adhesion reliability. For this reason, suitable seed layer materials are required for adhesive copper plating. As a requirement of a suitable seed layer material, contact resistance between the seed and the ITO is also important, as well as the adhesion, since a high series resistance results in a low fill factor. In this work, we applied copper alloy (Cu–X) materials as a seed layer that was deposited by co-evaporating copper with other metals. The contact resistivity (ρc) values of the Cu–X seed layer and copper-plated contact with the Cu–X seed layer (Cu–X/Cu) on the ITO layer were evaluated by the transfer length method (TLM). Also, tape tests were carried out to check the adhesion of the Cu–X/Cu contact.