Researchers from Fraunhofer-Gesellschaft will be demonstrating how laser technology can contribute to optimizing the manufacturing costs and efficiency of solar cells at Laser 2009 in Munich on June 15 to 18.

At the Fraunhofer Institute for Laser Technology ILT in Aachen, researchers are developing technologies now that will allow faster, better, and cheaper production of solar cells in the future.

At “Laser 2009” in Munich, the researchers will be demonstrating how lasers can drill holes into silicon cells at breathtaking speed: The ILT laser system drills more than 3,000 holes within one second. Because it is not possible to move the laser source at this speed, the experts have developed optimized manufacturing systems which guide and focus the light beam at the required points.

“We are currently experimenting with various laser sources and optical systems,” Dr. Arnold Gillner, head of the microtechnology department at the Institute for Laser Technology explained. “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.”

The tiny holes in the wafer--their diameter is only 50 micrometers--open up undreamt-of possibilities for the solar cell developers. “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% in industrially-produced emitter wrap-through (EWT) cells, with a yield of one-third more than classic silicon cells,” Gillner explains.

Drilling holes into silicon cells is only one of many laser applications in solar cell manufacturing. 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 optimized in the future.

One example would be selective laser soldering, which improves the quality of contacting and reduces its manufacturing costs. In selective laser soldering, the contacts are pressed on to cells with compressed air then soldered with a laser. The mechanical stress approaches zero and the temperature can be precisely regulated, thereby resulting in optimal contacts with no accidental breakage in production.

Laser technology is also helping to optimize the manufacture of thin film solar cells. One obstacle in thin film’s wider use is its low efficiency (five to eight percent) compared to its high production cost. ILT researchers have developed a 400-watt ultrashort pulse laser that processes thin-film solar modules ten times faster than conventional diode-pumped solid-state lasers.

“The ultrashort pulse laser is an ideal tool for ablating thin layers: It works very precisely, does not heat the material and, working with a pulse frequency of 80 MHz, can process a 2-by-3 meter glass panel in under two minutes,” Gillner reports. “The technology is still very new, and high-performance scanning systems and optical systems adapted to the process must be developed first. In the medium term, however, this technology will be able to reduce production costs.”

“Lasers simplify and optimize the manufacture of classic silicon and thin-film cells, and they allow the development of new design alternatives,” Gillner continues. “And so laser technology is making an important contribution towards allowing renewable energy sources to penetrate further into the energy market.”


-  Katrice Jalbuena

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Sources:

¹ http://www.fraunhofer.de/EN/press/pi/2009/05/PressRelease29052009.jsp
² http://www.fraunhofer.de/EN/