AbstractIn this paper, we investigate the mechanisms leading to rear reflectance losses in i-PERC type solar cells by means of reflectance measurements, scanning spreading resistance microscopy (SSRM), and transmission electron microscopy (TEM). Using 2μm sputtered (PVD) AlSi12.7% (eutectic composition) it is found that the interaction between Si present in the sputtered mixture and the rear dielectrics upon contact firing leads to a large drop in rear reflectance even without any laser ablated contact openings. On the other hand, in the case of local Al-BSF formation with pure PVD Al, it is shown that the presence of Si on top of the rear dielectrics, coming from Si diffusion into the Al layer with alloying, leads to parasitic absorption which contributes almost entirely to the measured drop in rear reflectance.