At present, solar cells based on crystalline silicon wafers make up more than 90 percent of all solar cells produced worldwide. The bottle neck in the production of highly purified silicon has led to many activities centered around this material. In addition to expanding the production capacity in industry, solar cell manufacturers and researchers are also forging new paths in the use and optimization of the material. Against this background, Fraunhofer ISE (Freiburg, Germany) is strengthening its activities in the area of materials research.

Now supplemented by the new laboratory "SIMTEC - Silicon Materials Technology and Evaluation Center", Fraunhofer ISE performs process steps across the whole solar value chain - from materials to modules - in the field of applied research. The new SIMTEC focuses on silicon crystallization and wafer technology as well as crystalline silicon thin-film technology. Starting with various sources of silicon feedstock, the work ranges from multicrystalline block crystallization, block shaping through to wafering and - as a new technology in photovoltaics - silicon epitaxy for crystalline silicon thin-film wafer equivalents.

Crystallization of silicon blocks sets the course for solar cell efficiency

"On the long journey from the raw silicon material to the finished photovoltaic module, the crystallization of silicon blocks is a decisive process step", explains Dr. Stefan Reber, head of the group Crystalline Silicon - Materials and Thin film Solar Cells. "In this step, the course is set, so to say, for the solar cell efficiency. With SIMTEC, we now have the necessary equipment at our disposal to intensively carry out work on the current and future topics on the material side."

Metallurgical grade silicon for cheaper solar cells

This includes considering lower-cost metallurgical grade silicon and its use for the production of solar cells, after the metal impurities from the material have been removed. In addition to crystallization and wafering, the researchers at SIMTEC in Freiburg also are active in the field of crystalline silicon thin-film technology. This area shows promise for building a bridge between the high efficiencies of the conventional wafer technology and the low material consumption of the thin-film technology - at much lower manufacturing costs.

"Silicon epitaxy plays a central role in this technology. At SIMTEC in our new 600m² laboratory, we can investigate and optimize the crystalline silicon epitaxy process in all aspects through to the production suitability", Reber emphasizes. As a result, after almost twenty years of research and development, Stefan Reber’s team aims to make this technology ready for the market within the next two years. The equipment at SIMTEC was supported by funds from the German Ministry for the Environment, Nature Conservation and Nuclear Safety. The project work is supported by funds from the Fraunhofer-Gesellschaft.

2008-10-23 | Courtesy: Fraunhofer ISE | solarserver.com © Heindl Server GmbH