Black power: Dark solar cell smashes record for absorbing photons

We all know how hot we feel wearing a black shirt on a sunny summer day. Does the same thing happen to a solar cell? Duh! Greater energy efficiency is on the way.

Black Beauty: Natcore technician Rich Topel admires a wafer of "absolute black" silicon, which absorbs so many photons it could become the workhorse of the solar industry.

We all know how hot we can feel wearing a black shirt on a sunny summer day. The shirt absorbs more photons than a white garment would. We feel those photons as heat.

Does the same sort of thing happen with solar cells? Duh! Solar cell makers have long used dark colors - often blue - to increase the cell's photon sucking power and thus to improve the cell's energy production. In photovoltaic energy,  those photons become electricity.

Now, Natcore Technology Inc. has developed a solar cell that's so black it absorbs practically every photon that hits it, smashing the sponging record.

Natcore, based in Red Bank, N.J., says that its "absolute black" solar cell absorbs 99.7 percent of the photons from most of the light that hits it. Typical solar cells in use today absorb around 96 percent, the company infers in a press release.

That extra amount might not sound like a lot, but it can represent big strides in solar electricity economics, the company claims. It would increase the efficiency of a solar cell by 3 percent, which in the energy numbers and ROI game can make the difference in whether or not a solar installation is viable.

Natcore claims that panels made from absolute black solar cells would produce "significantly more energy on a daily basis" not only because they would absorb more photons in general, but also because they would perform better in the morning, afternoon and on cloudy days, when less sun directly hits a solar panel.

"With solar cells, 'blackness' is highly desirable because it indicates that incident light is being absorbed for conversion to energy rather than being reflected and thus wasted," the press release states.

The Red Bank, N.J. company achieved "absolute black" by coating a silicon wafer. First it etched "nanoscale pores" into the wafer using a liquid solution at room temperature. It next filled the pores via a liquid phase deposition process and then "over-coated them with silicon dioxide," the press release explains. It developed the technology as part of its work with black silicon patents licensed from the U.S. Department of Energy's National Renewable Energy Laboratory.

Natcore CEO Chuck Provini said the company is working with two equipment manufacturers to design a production tool that could make 2,000 black silicon wafers per hour.

"When the design is completed, we'll take orders for the tool," he said in the press release. "We have already begun talking with potential customers in Italy, China and India."

Solar cells are rudimentary semiconductors. They are much bigger than the chips that go into computers, explained Natcore co-founder and chief technology officer Dennis Flood. Typically one silicon wafer yields one 5- or 6-inch  solar cell, which manufacturers then join with other cells into a solar panel, he said.

Photo from Natcore.

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