Rear passivated point contact solar cells achieving more than 19.3% conversion efficiencies were developed by using 156x156mm, p-type single crystalline silicon wafers. Full area aluminum back surface field solar cells, fabricated with the same wafers exhibit only 18.6% conversion efficiency. Eight different specially formulated aluminum pastes, with varying electrical and surface properties, and varying reactivity of silicon atoms to aluminum matrix were evaluated. The pastes all contain non-leaded frits and the adhesion strength to the substrate of these pastes lies in the range from less than 20N to greater than 40N. The thicknesses of the back surface field (BSF) depend on the firing condition, as well as paste formulation, and range from 3.7μm to 7.5m. The extent of partial contact fill and cavity formation varied from paste-to-paste; was shown to be largely reduced with optimized firing conditions. A modified co-firing process was developed for the fabrication of rear local contacts without affecting the integrity of the front metal contact.

27th European Photovoltaic Solar Energy Conference and Exhibition; 608-613