A laser-based manufacturing process developed by the Fraunhofer ISE in Freiburg, Germany promises to revolutionise the photovoltaics market. For the first time point-contacted solar cells can be manufactured in series.
Currently, most solar cells have a wide-surface metallic contact, covering the entire back side of the silicon wafer and allowing electricity to flow from the cell to the electrode. This configuration limits efficiency. A more high-performance alternative is the Passivated Emitter and Rear Cell technology (PERC). This technology, which was developed in 1989 at the University of New South Wales, includes an additional reflective layer on the back side of the cell and thousands of electric contact points.
In a PERC cell, a very thin non-conductive layer is deposited on the underside of the cell between the contact layer and the silicon wafer. This layer acts as a mirror to reflect the share of sunlight, which has not been absorbed when penetrating the wafer, back into the silicon wafer. The front side also reflects this light back into the wafer, so that it is also captured in the silicon wafer and the efficiency level of the solar cell increases. Drawing the electricity from the wafer requires many small apertures in the non-conductive layer in order to establish contact between the electrode metal and the silicon wafer.
The Fraunhofer procedure creates each of these approximately 100,000 contacts per wafer with a single laser pulse and has enabled the first industrial mass production of PERC solar cells.