Novel metallization approaches with very low specific contact resistance for crystalline silicon solar cells

Abstract

In this paper some new approaches for the front side metallization of crystalline silicon solar cells are presented, targeting on dramatically reducing the specific contact resistance between the metal gridline and the n+ emitter layer. One of them is to use a blanket sputtered nickel film as the contact layer and screen printed silver lines as an etch mask to pattern the underlying nickel film. This approach ensures the use of high quality nickel film as a contact layer to reduce the specific contact resistance, and also avoids the use of standard photolithographic process to reduce the cost. In addition, it makes the nickel contact layer self-aligned with the silver gridline and permits immediate cell testing after firing. The experimental result shows that the specific contact resistance with this approach can be reduced by almost two orders of magnitude compared to only using screen printed silver gridlines. This may increase the absolute cell efficiency by up to 0.9%, as given by the PC1D modeling. In order to further reduce the process steps and the cost for introducing the nickel film contact layer, electroless plating and inkjet printing nickel nanoparticle inks to form the contact layer are also being developed.