Toothpaste inspires better solar panels, batteries at PARC

Engineers are making energy devices more efficient thanks to printing technology

By , IDG News Service |  Hardware, PARC, solar energy

They say inspiration can come from the most unlikely places. For a scientist at the Palo Alto Research Center, the Xerox-owned lab in Silicon Valley best known as PARC, it came from a tube of toothpaste.

The result is a new manufacturing method that can help make solar panels more efficient and increase the energy density of batteries.

It began when the lab was looking at ways it could use existing Xerox technology, like printing, in other areas. While watching the way the two or three materials help shape each other when they are squeezed through a toothpaste tube nozzle, an engineer had one of those "a-ha" moments.

By squeezing through a print nozzle a silver paste surrounded by a sacrificial material that would eventually get burned off, researchers found they were able to get a very fine silver line -- and in electronics, any type of fine, conducting line is usually good.

The sacrificial material shapes the silver as it comes out of the nozzle so the resulting silver line is 50 microns wide and 30 microns high (a micron is a thousandth of a millimeter) -- half the width and three times the height achieved when depositing silver on its own, said Scott Elrod , vice president and director of PARC's hardware systems lab where the work is being done.

"So this is a solar cell," said Elrod, showing a reporter a prototype made with the technology. The cell is covered with narrow grid lines that carry power but also lie on top of the photovoltaic material that converts light into electricity. Finer silver lines mean less of the solar cell's surface is covered and that means more power can be generated.

(See video of the printing technology and prototype solar cell on YouTube.)

"You can imagine a hundred megawatt production facility," said Elrod. "You drop in this kind of of printing technology in place of the conventional screen printing and you're up to a hundred and three, hundred and four, hundred and five megawatts and the cost for this technology is very similar to what it is for the conventional screen printing."The system is already in pilot production with an unnamed solar cell maker.PARC hasn't finished there. The same technology is being tried out in lithium ion batteries, which sit at the heart of electric cars, power tools, laptop computers and a myriad of other portable electronic gadgets.

Batteries generate electricity through an electron flow between a cathode and anode. The PARC researchers have been using their co-extrusion technology to make small channels in the cathode that allow the lithium ions to penetrate deeper.

"By doing that you can make the electrode thicker and as you make it thicker you basically make the energy density for the whole battery higher," said Elrod. "So instead of going a hundred miles on an electric vehicle battery you can maybe go a hundred and twenty miles. We think that the improvement is on the order of twenty percent."

The battery is still in the research stage, but the company has already come up with some prototype button cells. PARC is hoping the technology will be employed in electric car and power tool markets first.


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