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NREL developed the technology to grow high-quality silicon

Straight from Pure Silicon to High-Quality Crystal Silicon Film

ORNL developed the metal foil that has the correct crystal structure to support that growth.

And Ampulse is installing a pilot manufacturing line in NREL’s Process Development Integration Laboratory (PDIL), where solar companies test their latest materials and processes.

With knowledge and expertise acquired from the PDIL pilot production line, Ampulse plans to design a full-scale production line to accommodate long rolls of metal foil.

The Ampulse process “goes straight from pure silicon-containing gas to high-quality crystal silicon film,” said Brent Nelson, who runs the PDIL at NREL. “The advantage is you can make the wafer just as thin as you need it — 10 microns or less.”

Most of today’s solar cells are made out of wafer crystalline silicon, though thin-film cells made of more exotic materials like gallium, arsenic, indium, arsenide, cadmium, and tellurium are making a strong push into the market.

The advantage of silicon is its abundance, as it is derived from sand. Its disadvantage is that purifying it into wafers suitable for solar cells is expensive and energy intensive.

Manufacturers add carbon and heat to sand to produce metallurgical-grade silicon, which is useful in other industries, but not yet suitable for making solar cells. This metallurgical-grade silicon is then converted to pure trichlorosilane (SiCl3) or silane (SiH4) gas.

Typically, the purified gas is converted to create a silicon feedstock at 1,000 degrees Celsius (°C). This feedstock is melted at 1,414°C and recrystallized into crystal ingots that are finally sawed into wafers. Think of it as the Rube Goldberg approach to creating a solar cell.

Instead, the Ampulse process backs up two steps. Rather than create a feedstock, it works with the silane directly and grows just the needed silicon right onto a foil substrate.

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