The use of laser in the manufacture of solar cells

The use of laser offers new perspectives for the manufacture of solar cells: faster and more accurate than the conventional means of production, they can increase efficiency and reduce costs.

The Fraunhofer Institute will soon present its findings on the subject, on the occasion of the exhibition "Laser 2009" in Munich.

"Experts predict that the network will be achieved parity in a few years", says Gillner, Head of the Department of Microengineering of the Fraunhofer Institute. "This means that the costs and opportunities on the network will be the same for solar power than for conventionally produced electricity for households."

The use of laser in the manufacture of the cells could contribute to achieve this goal.

"The laser can work quickly, accurately and without contact," explains Gillner. "In other words, it is an ideal tool for the manufacture of fragile solar cells. In fact, lasers are used in production today, but much remains to be done to optimize the process."

At the Munich Fair, the team of Dr. Gillner will demonstrate a laser capable of drilling holes in the silicon cells at breakneck speed: 3000 holes per second. Because it is not possible to move the source of the laser with such speed, researchers have developed optimized production systems, which guide and concentrate the light on specific points.

"We are experimenting with the process with different sources of laser and optical systems," says Gillner. “Our objective is to increase the performances with 10,000 holes per second”.

Drilling small holes in the wafer with a diameter of 50 micrometers, offers unsuspected opportunities for developers of solar cells.

"Previously, electrical contacts were prepared on top of the cells. The holes allow you to move the contacts to the rear. The advantage is that the electrodes, which act like a “network sinks” and absorb the light, disappear.”

The performance is better: it is possible to increase by one third the efficiency of conventional silicon cells.

The principle itself remains unchanged. Only the shade of the electrodes on the surface is removed, which is enough to reinforce the effectiveness. With this technique, it is also possible to use "dirty" silicon, not purified, for solar cells that have low electrical properties but would be much cheaper.

The laser offers other opportunities for the production of solar cells: new methods are developed, particularly by European teams (Solasys Project). They relate to the drilling and structuring of the surface of silicon, the isolation of cell borders, welding modules. This, by further reducing manufacturing costs.

For example, selective laser welding avoids the use of mechanical press and the use of heating, often responsible for a high rate of breakage during production. The thin-film cells should also derive large benefits from such research.

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