A new back metallization concept for PERC cells

The aim of the present work is to develop an alternative backside metallization scheme for PERC cells. The study is motivated by accessible savings in metallization costs, the availability of highly productive manufacturing equipment and the expected improvement of cell performance. The new backside metallization consists of a ca. 1 - 1.5 μm thick (Ag)/Al/NiV PVD back metal layer stack. This stack is fully replacing the state-of-the-art screen printed Al/Ag-paste backside. In the experiments, the new metallization is fully deposited on an AlO
_x
/SiN
_x
PERC cell backside, utilizing high-productivity, low cost architectural glass type sputter coaters, that can have a productivity of up to 10,000 wph. Different ways of laser contacting are tested and compared. The results are analyzed and compared with standard monocrystalline reference PERC cells with screen printed metallization. Without any further optimization, the presented first results are showing an average cell efficiency of 20.54 %. The analysis of the cell parameters shows that the major differences stem from lower cell V
_oc
compared to the reference cells, potentially attributable to limited local BSF forming. Optical analysis shows that a thin PVD Ag mirror can improve Jsc by +0.43 mA/cm
²
and cell efficiency by +0.24% absolute. In combination with alternative routes for local BSF forming (PERL), the presented metallization scheme forms an interesting candidate for future solar cell metallization with higher cell efficiency and lower cost. The subsequent cost analysis shows, that paste savings can be considerable, especially if a further replacement of the front side Ag busbars by shadow mask structured NiV solder layers is conducted. The solderability of the NiV solder pads has been tested on a standard cell stringer and good adhesion parameters have been found.