Rear Surface Passivation for Industrial Solar Cells on Thin Substrates

The use of hydrogenated silicon nitride is one of the most significant technological evolutions that has taken place in solar cells industry, due to its ability to act simultaneously as antireflective coating as well as a source of hydrogen for surface and bulk passivation. These very same properties make it an ideal candidate for rear surface passivation in structures with local contacts, yet its application has led so far to results below expectation. This work analyses limits and phenomena that prevent the use of standard nitride as rear surface passivation layer in commercial solar cells and presents a convenient process that can be used to overcome these problems and allows the fabrication of industrial, fully screen printed, PERC-type solar cells on ultrathin substrates. By means of this technology the cell's open circuit voltage shows a significant improvement with respect to the conventional aluminum BSF and is retained all the way down to 100 mum thick devices