Does Silicon Availability Threaten a-Si Growth?

With their lower-cost manufacturing methods and freedom from silicon shortages, thin-film solar cell technologies have occupied a growing slice of market share, and a great deal of buzz continues to surround amorphous silicon (a-Si), in particular.

But considering that the popularity of thin film was so tightly linked to the limited availability of the polysilicon and silane required for the manufacture of crystalline wafer cells, what is in store for a-Si now that supply shortages no longer constrain the silicon wafer market?

"Because there is a plentiful supply of polysilicon and silane in the supply chain now, it will greatly slow down what people were anticipating would be fast growth for amorphous silicon," says Lita Shon-Roy, senior managing partner at market research firm Techcet Group LLC.

Both the solar market's overall slowdown and polysilicon providers' expanded capacities contributed to the current polysilicon oversupply, which Shon-Roy expects will last for the next few years.

Typical contract prices for silicon have plummeted from approximately $180 per kg to $110 per kg, with spot pricing even lower. Although existing contracts have prevented many wafer manufacturers from reaping the benefits of the price drops, contract renegotiations are becoming increasingly popular, she adds. Other manufacturers are opting to buy silicon on the open market for an astounding $50 per kg.

As a result of this enormous shift, market share for a-Si, which is currently in the single digits, is now generally expected to remain well below 20% for the next five years.

In addition, low conversion efficiency, which was previously often viewed as the most potent growth-limiting factor for a-Si and other thin-film technologies, might now rank as the less important concern.

However, Shon-Roy notes that although a-Si manufacturers certainly still face challenges in increasing efficiency, many companies have made notable strides recently.

"Conversion efficiencies today are somewhere between six percent and eight percent in actuality, but manufacturers should be able to reach upwards of 12 percent to 15 percent in the next five years," she says.

Market-penetration advantages will likely be realized once several a-Si cell manufacturers cross that 12% to 15% threshold. "But depending on how you do the math, even at 10 percent efficiency, the technology can still work less expensively than silicon wafer-based technology," she adds.

Nonetheless, Shon-Roy says a-Si boasts the most cost-reduction potential of the major thin-film technologies. As was the case in the semiconductor industry, this distinguishing quality is likely to prove even more important as the solar manufacturing industry grows, and will help propel a-Si's expansion.

Cadmium telluride solar cells, in contrast, currently hold about 5% of current market share and may gain another 5% over the next five to six years. This technology's growth, however, remains "somewhat limited" because of innate technological shortcomings and a toxicity stigma, says Shon-Roy.

In addition, "From a supply-chain standpoint, cadmium and tellurium are metals that are not as abundant in availability as materials like aluminum and silicon," she says.

Generally, within a-Si and beyond, thin-film manufacturers that can smartly engage in materials substitution can be reasonably expected to thrive in the new market. "The name of the game for thin-film production is that the materials that are going to be used need to be relatively available and inexpensive," Shon-Roy stresses.

Thin-film cells originally incorporated indium tin oxide as the transparent conductor, for example. This material was subsequently replaced with more readily available and less expensive aluminum zinc oxide, she points out. Although a similarly obvious replacement may not be found again, the quest for such measures remains ever-important.

Meanwhile, as a-Si manufacturers grapple with the new market challenges associated with the silicon glut, an old and formidable hurdle still lingers.

"I think the biggest obstacle for amorphous silicon is its track record," Shon-Roy says. With few completed installations in the field in comparison to other technologies, and relatively short operating histories for most of these existing systems, many utilities and other key purchasers remain wary of a-Si, despite what is generally a lower price tag.

But ultimately, inevitable gaps between lab performance and performance in the field - a classic developing-technology issue to which a-Si has not been immune - can be overcome and help boost a-Si's reputation.

According to Shon-Roy, one recent study showed that the majority of lab-developed technologies will attain 80% of their laboratory results once they reach wide-scale high-volume production, and that any technology takes at least five years before it approaches the upper end of what it can achieve.