Evergreen Solar Reports Latest String Ribbon Advance

February 03, 2004 by Jeff Shepard

Evergreen Solar Inc. (Marlboro, MA), a developer, marketer and manufacturer of photovoltaic products, announced that it has successfully completed a prototype research project for its proprietary String Ribbon™ technology for manufacturing solar cells; enabling the growth of four silicon ribbons from a single furnace.

The research project was co-funded by a three-year, $2 million grant from the Advanced Technology Program of the National Institute of Standards and Technology. The completed project demonstrated a significant enhancement over Evergreen's double String Ribbon technology, which the company announced a little over one year ago.

"It is widely recognized that growing silicon ribbons directly from the melt in a furnace has excellent potential to achieve lower costs in producing silicon solar cells," said Evergreen Solar Chief Technology Officer Jack Hanoka. "What we've been able to demonstrate here is not only growing four ribbons from a single furnace, but an entirely new, dramatically simpler approach to crystal growth."

In the String Ribbon technique, originally developed at MIT and commercialized and improved at Evergreen Solar, high-temperature strings are pulled vertically through a shallow silicon melt, and the molten silicon spans and freezes between the strings to form a ribbon of silicon. Each pair of strings produces a single ribbon. Long strings are unwound from spools; the melt is replenished; and the silicon ribbon is cut into strips for further processing, without interrupting growth. The String Ribbon can yield over twice as many solar cells per pound of silicon as conventional methods.