Metal pinning through rear passivation layers: Characterization and effects on solar cells

We investigate local defects in rear passivation layers, in which the metal is forming a contact to silicon pinning through an insulating layer. At first, we studied these contacts by measuring the layer resistivity of different dielectrics sandwiched between Al and Si. Our study includes the influence of parameters like the surface roughness, the metallization techniques and the post-metallization annealing. In addition, we propose a characterization of these contacts on solar cell level, using photoluminescence-imaging performed before the finalization of the rear contacts. A good correlation between the contacts and the dark saturation current density suggests that these contacts can harm the rear surface passivation quality.