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Lasers to make solar cells more efficient

Posted: 04 Jun 2009     Print Version  Bookmark and Share

Keywords:laser technology  solar cells  optical systems  silicon cell 

Researchers from the Fraunhofer Institute for Laser Technology will be demonstrating how laser technology can contribute to optimising the manufacturing costs and efficiency of solar cells at Laser 2009 in Germany, June 15 to 18.

At Laser 2009, the researchers will show how the ILT laser system drills more than 3,000 holes within one second. The scientists have developed optimised manufacturing systems to guide and focus the light beam at the required points.

The laser beam is guided and focused by means of a process adapted manufacturing system. This allows thousands of holes to be burned into a silicon wafer in one second.

The laser beam is guided and focused by means of a process adapted manufacturing system. This allows thousands of holes to be burned into a silicon wafer in one second.

The laser beam is guided and focused by means of a process adapted manufacturing system. This allows thousands of holes to be burned into a silicon wafer in one second.

"We are currently experimenting with various laser sources and optical systems," explained Dr. Arnold Gillner, head of the microtechnology department at the Fraunhofer Institute for Laser Technology in Aachen, Germany. "Our goal is to increase the performance to 10,000 holes a second. This is the speed that must be reached in order to drill 10,000 to 20,000 holes into a wafer within the cycle time of the production machines."

"Previously, the electrical contacts were arranged on the top of the cells. The holes make it possible to move the contacts to the back, with the advantage that the electrodes, which currently act as a dark grid to absorb light, disappear. And so the energy yield increases. The goal is a degree of efficiency of 20 per cent in industrially-produced emitter wrap-through (EWT) cells, with a yield of one-third more than classic silicon cells."

Drilling holes into silicon cells is only one of many laser applications in solar cell manufacturing that is being developed. In the EU project Solasys—Next Generation Solar Cell and Module Laser Processing Systems—an international research team is currently developing new technologies that will allow production to be optimised in the future. ILT in Aachen is coordinating the Rs.40.07 crore (six million euro) project.

"We are working on new methods that make the doping of semiconductors, the drilling and the surface structuring of silicon, the edge isolation of the cells, and the soldering of the modules more economical," project coordinator Gillner explained. For example, 'selective laser soldering' makes it possible to improve the rejection rates and quality of the contacting, and so reduce manufacturing costs. Until now, the electrodes were mechanically pressed onto the cells, and then heated in an oven.

"But silicon cells often break during this process," Gillner knows. "Breakage is a primary cost factor in production." The 'selective laser soldering' method presses the contacts on to the cells with compressed air and then they are soldered with the laser. The mechanical stress approaches zero and the temperature can be precisely regulated. The result equates to optimal contacts and almost no rejects.

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