Metallization improvement on fabrication of interdigitated backside and double sided buried contact solar cells

Metallization based on electroless metal plating of nickel and copper is a simple, cost-effective process used in the fabrication of Buried Contact silicon solar cells. Whereas the electroless Ni–Cu metallization scheme works well for metal deposition on early Buried Contact solar cells, in which deposition was required only on phosphorus diffused contact regions, more care is required for advanced Buried Contact solar cell designs that require simultaneous deposition on to both phosphorus and boron diffused contact regions. In this paper, we examine two key issues related to the metallization in these solar cells. Firstly we demonstrate an improved buffered hydrofluoric acid etch process for simultaneous removal of borosilicate and borophosphosilicate glasses from the contact regions prior to electroless deposition of nickel with good etch selectivity against silicon dioxide masking films. Secondly, we demonstrate an improved process for nucleation of the nickel layer on both phosphorus and boron diffused contact areas based on immersion palladium chloride activation of the plating surfaces. N-type double-sided buried contact solar cells metallized by processing introduced in this study show improvement on absolute efficiency of more than 3%.