Harnessing solar power, on a small scale

A team at MIT is working on thin, flexible, pocket-size panels

By Karen Weintraub
Globe Correspondent / July 18, 2011

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No thicker than a piece of paper - because it practically is a piece of paper - a solar panel created by an MIT researcher can be shoved into a pocket or made into a paper airplane, and it will still create energy when exposed to sunlight.

The trick is in the way it is made. The panel is printed like ink onto a sheet of paper. Even folded up like a letter, it retains its ability to convert light to electricity.

With her colleagues, Karen Gleason, a professor of chemical engineering at the Massachusetts Institute of Technology, published a paper last week in the journal Advanced Materials, demonstrating how they created a solar panel by printing tiny, lightweight layers of electrodes and semiconductors on a piece of paper.

Traditional solar panels are made through high-heat or wetting processes that would fry or soak paper. Gleason and her collaborators have developed a method they call vapor printing, which allows them to lay down the conductive material at moderate temperatures. She compared it to the process used to create the metallic inner layer of a potato chip bag.

Printing solar cells onto something as cheap, lightweight, and easy to manipulate as paper, rather than using heavy glass panels, means the process might be used to give cellphones, calculators, and other small electronic devices the ability to generate at least some of their own power.

The same technique could be used on fabric to make, say, curtains that can collect and generate energy from the sun, said Gleason, who is also associate dean of engineering for research.

Gleason’s work, along with other solar-energy research at MIT, is funded by the Italian energy company Eni. Researchers around the world are searching for ways to advance photovoltaic technology, from laying down single crystals to films of living cells. Their aim is to find a clean source of energy with the reliability and low cost of the power grid, but which is also flexible and cheap enough to be used on remote devices and in the developing world.

Gleason’s edge is that she can print her cells quickly and inexpensively, said Shriram Ramanathan, an associate professor of materials science at Harvard University.

Max Shtein, an associate professor of materials science and engineering at the University of Michigan, said the work has potential for making textiles extremely water-repellent. They could also serve as a surface for the materials used to create organic semiconductors, which are being explored for their potential to build devices that are flexible or even transparent, he said.

Shtein said he’s particularly interested in the new material’s ability to be “printed’’ at relatively low temperatures, as well as to form films that are flexible and conform to the smallest surface irregularities, which “can be a big help in prolonging the lifetime of organic [and other] semiconductor devices,’’ he wrote in an e-mail.

The efficiency of the material - its ability to convert sunlight quickly into energy - is not nearly as good as a conventional solar panel’s. But Ramanathan said there is plenty of time to improve efficiency.

“In such early-stage, proof-of-concept [research], typically the efficiencies cannot compare with well-developed techniques,’’ he said.

Gleason said she has begun testing ways to improve efficiency by making simple changes in the pattern in which the layers of electrodes and semiconducting material are laid down. She has other improvements planned, as well.

Her cell does not have to reach the efficiency of a giant solar panel, she said, because it would be used to power a single device, rather than feed into a grid.

She would also like to shrink the size, Gleason said. Right now, it takes a piece of paper the size of a mouse pad to fuel a simple LED display. Her aim is to shrink it to the size of a business card.

The process could be an end-run around the economic factors that have limited the development of photovoltaics, Gleason said. “There’s very imaginative things that you can do with the technology,’’ she added.