Joseph von Fraunhofer Prize 2016: Laser-based production process for high efficiency solar cells wins award

Solar cell manufacturers can integrate the laser procedure in existing production processes
Solar cell manufacturers can integrate the laser procedure in existing production processes

Ralf Preu, Division Director of PV Production Technology and Quality Assurance at the Fraunhofer Institute for Solar Energy Systems ISE (Freiburg, Germany), and his colleague Jan Nekarda have been awarded the Joseph von Fraunhofer Prize 2016 for the development of Laser-Fired Contact (LFC) technology, enabling the manufacture of more efficient solar cells at lower cost.

At the annual meeting of the Fraunhofer-Gesellschaft on May 10th, 2016 in Essen (Germany), the Prize was presented to Ralf and Jan.

“We are delighted to receive this distinguished prize, which is not only a recognition of our work but also shows the innovative strength of the German and European photovoltaic industry,” says Ralf Preu.

 

First industrial mass production of PERC solar cells

Today most solar cells are equipped with a wide-surface metallic contact, covering the entire backside of the silicon wafer and allowing electricity to flow from the cell to the electrode. However, this configuration limits efficiency. A more high-performance alternative, discovered in 1989, is the Passivated Emitter and Rear Cell technology (PERC). In contrast to conventional cells, this technology includes an additional reflective layer on the backside of the cell and thousands of electric contact points. The LFC process developed by the Fraunhofer researchers has enabled the first industrial mass production of PERC solar cells.

A very thin non-conductive layer is deposited on the underside of a PERC solar cell between the contact layer and the wafer. Acting as a mirror, this layer reflects the share of sunlight not absorbed when penetrating the wafer back into the silicon wafer. Since the front side also reflects this light back into the wafer, 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 LFC procedure creates each of these approximately 100,000 contacts per wafer with a single laser pulse.

 

Laser light effect must be limited to between 50 and 2,000 nanoseconds

“The challenge was to coordinate the pulses in such a way that contact is completely established, while damage to the silicon is kept to minimal levels. Here it’s crucial that the laser light effect is limited to between 50 and 2,000 nanoseconds,” explains Dr. Jan Nekarda, group manager at the Fraunhofer ISE. An innovative system for guiding the laser beams makes it possible to create all the contacts in approximately one second.

“PERC solar cells made this way have an improved efficiency level of one percent absolute. With today‘s solar cell efficiency of approximately 20 percent, that’s about five percent relative. We gain an additional two percent in the system, which means we increase the overall energy yield by seven percent,” says Ralf Preu.

 

Successful Implementation in the industry

Solar cell manufacturers can integrate the laser procedure in existing production processes. According to company information, Hanwha Q Cells has already made 20 million cells using LFC technology since beginning production. Companies around the world have in the meantime put PERC technology into mass production.

Ralf Preu: “In the current year alone manufacturers have invested more than 200 million Euros in the implementation. This finally means the establishment of the next evolutionary stage of the silicon solar cell.”

Ralf Preu and Jan Nekarda received an award once before for their innovative Laser Fired Contact (LFC) technology. Together with a colleague, they received the European science prize “Innovation Award Laser Technology 2014”.

 

2016-05-11 | Courtesy: Fraunhofer ISE | solarserver.com © Heindl Server GmbH

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