SolarWorld has been one of the largest manufacturers of solar silicon wafers worldwide, and the company has produced a range of both mono-crystalline and multi-crystalline solar wafers. In this way, SolarWorld is positioned to meet customer-specific requirements. In recent years, it has invested more heavily in new, more cost-effective silicon-crystallization technologies.
Wafers are further processed to make solar cells – not only within the company but also by customers worldwide.
At the U.S. headquarters plant in Hillsboro, Oregon, the company historically has concentrated on producing mono-crystalline technologies. The know-how embedded in the U.S. branch of the company is based on more than 35 years of experience.
The company’s counterpart division in Freiberg, Germany, produces wafers and ingots exclusively from poly-crystalline, providing the overall company with the flexibility it needs to maximize technological and market requirements.
In the U.S. market, SolarWorld has applied the Czochralski method to produce its mono-crystal ingots. Within a furnace, a seed crystal featuring the desired crystal orientation is lowered down atop molten silicon. Under the right conditions, high-purity silicon begins freezing onto the seed while matching the orientation. The seed and silicon crucible are turned in opposite directions, and the seed is elevated, or pulled, to form a cylindrical crystal – like pulling a candle from melted wax. It takes about 3½ days to produce a single crystal of about 5 feet long and 8 inches wide.
In the poly-crystalline process, silicon, melted inside square molds, is allowed to freeze from the bottom up. As it returns to a solid form, the silicon forms a patchwork of crystal lattices, providing the resulting blocks with a poly-crystalline pattern.
Both types of ingots are then sliced into very thin discs, or wafers, with help from wire-cutting technology. After cleaning and intensive final checks are completed, mono-crystalline and poly-crystalline wafers from the basis for production of solar cells. The physical semiconductor quality determines the attainable efficiency in the manufacture of the solar cells.