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black silicon from NREL and Natcore
black silicon from NREL and Natcore

Clean Power

Move Over, Orange: Copper Is The New Black (Silicon)

Solar innovator Natcore and NREL team up to push the cost of black silicon solar cells down, down, down with new copper based catalytic process.

The last time we checked in on Natcore, the solar cell company was working on a low temperature process for pushing down the cost of its cutting edge black silicon solar cell. In the latest twist, Natcore has pulled a switcheroo on the catalyst used in the manufacturing process, which should help push costs down even farther.

black silicon from NREL and Natcore

Black silicon (cropped) via Wikimedia Commons.

Black Silicon: What Is That?

For those of you new to the topic, black silicon appears black because it is etched with nanoscale spikes. The spikes increase the surface area available for harvesting solar energy, so that gets you a more efficient silicon solar cell.

That also gets you a problem, which is how to rein in the cost of making all those little spikes.

As described by the folks at Natcore, the process involves etching with metal particles, typically silver. That’s a nice move from earlier attempts using gold (gold = $3,000 per ounce, silver = $20).

However, when you get into utility scale solar installations, the cost of all that silver is going to add up.

Super Cheap Black Silicon

Natcore co-founder Andrew Barron is a professor at Rice University, so it won’t surprise you to find that his Rice lab factored into the new improved catalyst.

The research team focused on copper, which at 20¢ per ounce beats silver by a mile, let alone gold.

Don’t get too excited because, by Natcore’s calculations, using copper instead of silver would barely make a difference in the cost of the manufacturing process for a single solar cell. The savings comes out to less than a penny per cell.

No wait, go ahead and be excited because when you tote up that savings for a utility scale installation, you get a much more impressive figure. Natcore uses the example of $100,000 in savings for a 100 megawatt facility.

Here’s how the black silicon magic happens (break added):

The chemical stew that makes it possible is a mix of copper nitrate, phosphorous acid, hydrogen fluoride and water. When applied to a silicon wafer, the phosphorus acid reduces the copper ions to copper nanoparticles.

The nanoparticles aid in removing electrons from the silicon wafer’s surface, thereby oxidizing it. The oxidized silicon is dissolved by the hydrogen fluoride, resulting in a process that forges inverted pyramid-shaped structures into the silicon.

The result is a form of black silicon that gets those little spikes down to the scale of 590 nanometers in length.

According to Natcore, this surface reflects less than one percent of the light that hits it (.96% to be precise), compared to almost 40 percent for a plain silicon wafer.

For those of you keeping score at home, you can find the research at the Royal Chemical Society’s Journal of Materials Chemistry A under the title “Anti-reflection layers fabricated by a one-step copper-assisted chemical etching with inverted pyramidal structures intermediate between texturing and nanopore-type black silicon.”

You can forget about holding your breath on this one because Natcore isn’t nearly ready to get the process into commercial play. According to Barron, the next steps are to compress the time needed for the process, tweak it so that no copper is left on the silicon at the end (that will help extend the lifespan of the solar cell), and figure out a way to prevent the nanoscale spikes from weathering.

We Built This Black Silicon!

Natcore has been all over this black silicon thing like white on rice, with a little help from us taxpayers so group hug. The black silicon patents at the heart of Natcore’s efforts come from the National Renewable  Energy Laboratory.

Late last year the company also announced another line of progress on reducing solar cell manufacturing costs, a low-temperature laser etching process. Aside from eliminating the costs associated with a high-temperature furnace, the new process also reduces hazardous waste byproducts.

As for incorporating the black silicon surface into a solar cell, we’ve also been following black silicon efforts in Germany along with our sister site PlanetSave.

The last time we checked, researchers at Fraunhofer ISE of Germany and Aalto University of Finland got their cell up to 18.7% efficiency.

 

That broke the previous record of 18.2% held by, you guessed it, the National Renewable Energy Laboratory so game on.

Meanwhile, don’t forget about black metals. The idea is to deploy the plasmonic effect to create nanoscale structures in metals that can harvest solar energy all up and down the spectrum.

Don’t forget that group hug, either. The Energy Department’s Lawrence Livermore National Laboratory has been pursuing the black metals angle, with the ultimate aim of making solar energy cost-competitive and affordable just about anywhere in the US, not just in prime solar locations.

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Written By

Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

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