Fraunhofer ISE develops new photovoltaic technologies

GERMANY: Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have developed new methods and cell concepts for the manufacture of n-type silicon solar cells. As a result, higher efficiencies and power production levels are also possible for commercial solar cells. The prototype exceeded an efficiency of 23 percent.

"Most commercial silicon solar cells are currently p-types," Fraunhofer ISE’s group manager Dr. Martin Hermle explains the difference between the new technology and current products.

"But the new n-type silicon used for the novel solar cell structures developed at ISE has better properties for photovoltaic electricity production, such as greater tolerance for most impurities. In practice, there are two options: either greater efficiency, or lower manufacturing costs because you can use less expensive silicon."

In addition, p-type Czrochalski (Cz) silicon suffers from light-induced degradation, which does not occur with n-type silicon.

Silicon solar cells consist of two areas with different thicknesses for different conduction: n stands for negative, p for positive. The thicker layer, the substrate material, is considered the base and determines the cell's type –- such as p-type for conventional solar cells.

Such cells have a p-type base and a thin n-conductive layer -– the emitter, or the charge carrier. In n-type solar cells, the emitter is p-doped, either through boron diffusion or the addition of aluminum.

For some time, experiments have been conducted on n-type silicon as a base material, but production technology was very complicated. For instance, the main problem in using n-type solar cells, in which the emitter is on the side facing the sun, was the passivation of the emitter, which was usually doped with boron.

Such surfaces cannot be optimally passivated with conventional layers, such as silicon oxide SiO2 or silicon nitride SiNx. In collaboration with the Technical University of Eindhoven, the problem of front passivation was solved through the use of aluminum oxide Al2O3.

Jan Benick, who is working on his doctorate in the group for high-efficiency silicon solar cells, managed to develop a highly efficient cell process especially for n-type cells that uses boron diffusion to make the emitter; the efficiency is 23.4 percent on 2x2 cm² -– the highest efficiency ever reached for this cell type.

Christian Schmiga, project leader in the group for high-efficiency silicon solar cells, has also reached 18.2 percent efficiency on 12.5x12.5 cm² by using much simpler process stages close to industry practice, including a screen printing process to apply the aluminum alloy emitter.

Fraunhofer ISE continues to further develop process technology for n-type solar cells so that industrially manufactured silicon solar cells can reach efficiency rates exceeding 20 percent quickly.

Photovoltaics International's solar awards on May 28

Photovoltaics International, a leading source for technical manufacturing information and news concerning the solar industry, has partnered with the International Photovoltaic Equipment Association, PV Group, and Sun & Wind Energy among others to introduce the International Solar Technology Awards, a new set of industry awards recognizing significant achievements in the production of solar technology.

Nominations closed on April 15. Winners will be honored at the awards ceremony at Intersolar in Munich on May 28, 2009.

Unlike current industry awards that focus primarily on early stage solar technologies, the International Solar Technology Awards are designed to put the spotlight on companies spanning the manufacturing supply chain from raw materials to modules. Judges from Q-Cells, Suntech, Deutsche Solar, Moser Baer, Fraunhofer ISE and others will select award recipients on their efficiency advancements, improved design and processes.

The eight International Solar Technology Award categories are:

* Best Technical Product for Module Assembly.
* Best Technical Product for Thin-Film Module Manufacturing.
* Best Process Technology for c-Si Cell Manufacturing Lines.
* Best Technology for Silicon Feedstock and Wafer Processes.
* Best New Manufacturing Facility for Cells, Modules, Equipment and BOS Components.
* Best Region for Manufacturing Solar Technologies.
* Green Manufacturing Award.
* Industry Choice Award.

“We created the International Solar Technology Awards to serve as a catalyst for new business opportunities through enhanced industry visibility,” said David Owen, Managing Director of Photovoltaics International. “By bringing together some of the most prestigious names in the solar space, we strive to provide the solar manufacturing industry with an unbiased, well respected recognition to showcase industry leaders.”

To apply for The International Solar Technology Awards and to learn more on award criteria and benefits, visit: http://www.cellaward.com/.

If you are a member of the solar industry and would like to register to vote for The International Solar Technology Awards, visit http://www.cellaward.com/register_to_vote.