• Barr holds a sheet of paper that has had one of the layers of the solar cell printed on its surface

    Photo: Patrick Gillooly

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  • A paper solar cell, which has been laminated in plastic, is connected to an LCD screen to demonstrate that it is producing power from ambient sunlight.

    Image courtesy of the Gleason Lab

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  • A paper solar cell that has been repeatedly folded is illuminated from below and connected to a voltmeter to demonstrate its output (26 V).

    Image courtesy of the Gleason Lab

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  • After several more layers are deposited, the finished product is a flexible, foldable, bendable solar cell printed on paper.

    Photo: Patrick Gillooly

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While you’re up, print me a solar cell

New MIT-developed materials make it possible to produce photovoltaic cells on paper or fabric, nearly as simply as printing a document.


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The sheet of paper looks like any other document that might have just come spitting out of an office printer, with an array of colored rectangles printed over much of its surface. But then a researcher picks it up, clips a couple of wires to one end, and shines a light on the paper. Instantly an LCD clock display at the other end of the wires starts to display the time.

Almost as cheaply and easily as printing a photo on your inkjet, an inexpensive, simple solar cell has been created on that flimsy sheet, formed from special “inks” deposited on the paper. You can even fold it up to slip into a pocket, then unfold it and watch it generating electricity again in the sunlight.

A paper solar cell
Graduate student Miles Barr hold a flexible and foldable array of solar cells that have been printed on a sheet of paper.
Photo: Patrick Gillooly

The new technology, developed by a team of researchers at MIT, is reported in a paper in the journal Advanced Materials, published online July 8. The paper is co-authored by Karen Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering; Professor of Electrical Engineering Vladimir Bulović; graduate student Miles Barr; and six other students and postdocs. The work was supported by the Eni-MIT Alliance Solar Frontiers Program and the National Science Foundation.

The technique represents a major departure from the systems used until now to create most solar cells, which require exposing the substrates to potentially damaging conditions, either in the form of liquids or high temperatures. The new printing process uses vapors, not liquids, and temperatures less than 120 degrees Celsius. These “gentle” conditions make it possible to use ordinary untreated paper, cloth or plastic as the substrate on which the solar cells can be printed.

It is, to be sure, a bit more complex than just printing out a term paper. In order to create an array of photovoltaic cells on the paper, five layers of material need to be deposited onto the same sheet of paper in successive passes, using a mask (also made of paper) to form the patterns of cells on the surface. And the process has to take place in a vacuum chamber.

The basic process is essentially the same as the one used to make the silvery lining in your bag of potato chips: a vapor-deposition process that can be carried out inexpensively on a vast commercial scale.

The resilient solar cells still function even when folded up into a paper airplane. In their paper, the MIT researchers also describe printing a solar cell on a sheet of PET plastic (a thinner version of the material used for soda bottles) and then folding and unfolding it 1,000 times, with no significant loss of performance. By contrast, a commercially produced solar cell on the same material failed after a single folding.

“We have demonstrated quite thoroughly the robustness of this technology,” Bulović says. In addition, because of the low weight of the paper or plastic substrate compared to conventional glass or other materials, “we think we can fabricate scalable solar cells that can reach record-high watts-per-kilogram performance. For solar cells with such properties, a number of technological applications open up,” he says. For example, in remote developing-world locations, weight makes a big difference in how many cells could be delivered in a given load.

A paper solar cell circuit is dynamically folded and unfolded while the voltage is simultaneously measured on the meter. The paper photovoltaic is illuminated from below with simulated solar illumination.
Video: Advanced Materials/courtesy of the Gleason Lab

Gleason adds, “Often people talk about deposition on a flexible device — but then they don’t flex it, to actually demonstrate” that it can survive the stress. In this case, in addition to the folding tests, the MIT team tried other tests of the device’s robustness. For example, she says, they took a finished paper solar cell and ran it through a laser printer — printing on top of the photovoltaic surface, subjecting it to the high temperature of the toner-fusing step — and demonstrated that it still worked. Test cells the group produced last year still work, demonstrating their long shelf life.

In today’s conventional solar cells, the costs of the inactive components — the substrate (usually glass) that supports the active photovoltaic material, the structures to support that substrate, and the installation costs — are typically greater than the cost of the active films of the cells themselves, sometimes twice as much. Being able to print solar cells directly onto inexpensive, easily available materials such as paper or cloth, and then easily fasten that paper to a wall for support, could ultimately make it possible to drastically reduce the costs of solar installations. For example, paper solar cells could be made into window shades or wallpaper — and paper costs one-thousandth as much as glass for a given area, the researchers say.

For outdoor uses, the researchers demonstrated that the paper could be coated with standard lamination materials, to protect it from the elements.

Others have tried to produce solar cells and other electronic components on paper, but the big stumbling block has been paper’s rough, fibrous surface at a microscopic scale. To counter that, past attempts have relied on coating the paper first with some smooth material. But in this research, ordinary, uncoated paper was used — including printer paper, tissue, tracing paper and even newsprint with the printing still on it. All of these worked just fine.

The researchers continue to work on improving the devices. At present, the paper-printed solar cells have an efficiency of about 1 percent, but the team believes this can be increased significantly with further fine-tuning of the materials. But even at the present level, “it’s good enough to power a small electric gizmo,” Bulović says.

A paper solar cell
Barr places a sheet of paper with a mask on it into the vapor-printing chamber.
Photo: Patrick Gillooly

“I am very excited by what is being done” by the MIT team, says Peter Harrop, chairman of IDTechEx, which does research on printed electronics. He says that while most researchers have been focusing on large-scale solar installations that could feed into the electric grid, the potential for other applications “is at least as large. Here the key parameters are very different, with disposable consumer goods, wall coverings and other applications with limited life required.”

He adds, “The work at MIT … is therefore very important. To succeed it must promise low enough cost and low enough sensitivity to humidity.” Other attempts to create printable solar cells have been criticized for failing to meet these criteria, he notes.


Topics: Chemistry and chemical engineering, Electrical engineering and electronics, Energy, Eni, Innovation and Entrepreneurship (I&E), Materials science, Solar

Comments

photovoltaic cells on cheap and recyclable materials is a new and interesting platform for generating energy. Dr. Prem Raj Pushpakaran http://livedna.net/?dna=91.1166
I'd love to have retractable awnings on the back (west facing) side of my house that would both shade it and generate some of the power needed to cool it. At night or on cloudy days I could retract them. It would be an easy retrofit, without major rework required. I could also see it being useful for RVs, camping, festivals, disaster sites, etc...
Seems to me, that we're getting very close to being able to generate electricity for low power devices. Do we need our lighting/power systems to catch up with the concept of on-site power generation? 240v incandescent lightbulbs wont work with this. 5v or 12v would seem a better choice.
SO there is no more worries on battery down on my I PHONE. Well to pump the power to grid through this solar coating technology how much will be the size of the paper or plastic to be used to deposit solar cell substances on to the paper substrate. What is the maximum voltage this technology can avail for a 1 m ^2 paper.
We have already caught up. Incandesents need 60 full watts, and current CFLs are only 12-17. Also, voltage doesn't matter as much as the watts.
This is great! SO many ways it can be used!
That's a very nice technology, which we can definitely use in Arizona. Keep up the good work guys!! Very Exciting.
It's really exciting to see this new development! How durable will this be if they are able to place it on most any material? My hope is that this kind of breakthrough will help in lowering the cost of PV Systems. I installed solar electricity on my home about 3 years ago. It's great seeing the power meter turn backwards.
I try to keep track of stuff like this because it really makes me happy to hear of such advances as this one. They make my day. I mean I'm still in high school, but I'm in love with technology and this is just, for the lack of other words, "awesome" an achievement. Love it, the work that's been done on this, everything about it, except that it's not on the market yet. I could think of 20 applications for this right off the bat. Thanks for making my day. Oliver Baumbach
This is a really intereting concept, have you work out with suppliers for fabric. Our company is really interested in it, and would like to have further develop with your concept. Please reply us so we can discuss more detail. Thanks.
This is a really interesting concept, have you apply this on fabric before? Our company is interested in it and would like to have further development with your concept. Please reply us so we can discuss it in detail. Thanks.
This is very exciting reading - I hope to see the fruit of this research very soon! Many new possible applications for solar technology now beckon. Thank you for this great article!
This is great gift for the world , so many people could benefit from this technology. Imagine a world where people don't die in their homes because they can't afford heat ... brilliant guys
If they used leaf like folds and wrinkles when folded the power wont decrease so much Article: http://www.wired.co.uk/news/archive/2012-05/01/leaf-mimicking-solar-cells
Why not use this method to paint this material on buildings or cars. Making these objects self supporting.
We have come a long way since this article. So great to look back and see all the changes plus see the vast future potential of this amazing technology. Dr. Sam Korn http://printingimpression.net
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