Breakthrough solar cell lighter, thinner than soap bubbles

The researchers lift the entire parylene/solar cell/parylene stack off the carrier after the fabrication process is complete, using a frame made of flexible film. The final ultra-thin, flexible solar cells, including substrate and overcoating, are just one-fiftieth of the thickness of a human hair and one-thousandth of the thickness of equivalent cells on glass substrates—about 2μm thick—yet they convert sunlight into electricity just as efficiently as their glass-based counterparts.

No miracles needed

"We put our carrier in a vacuum system, then we deposit everything else on top of it, and then peel the whole thing off," said Wang. Bulovic stated that like most new inventions, it all sounds very simple—once it's been done. But actually developing the techniques to make the process work required years of effort.

While they used a glass carrier for their solar cells, Jean said "it could be something else. You could use almost any material," since the processing takes place under such benign conditions. The substrate and solar cell could be deposited directly on fabric or paper, for example.

While the solar cell in this demonstration device is not especially efficient, because of its low weight, its power-to-weight ratio is among the highest ever achieved. That's important for applications where weight is important, such as on spacecraft or on high-altitude helium balloons used for research. Whereas a typical silicon-based solar module, whose weight is dominated by a glass cover, may produce about 15W per kilogram of weight, the cells have demonstrated an output of 6W per gram, about 400 times higher.

Figure 2: Bulovic: It could be so light that you don't even know it's there, on your shirt or on your notebook. These cells could simply be an add-on to existing structures. (Photo: Joel Jean and Anna Osherov)

Still, this is early, laboratory-scale work, and developing it into a manufacturable product will take time, the team said. Yet while commercial success in the short term may be uncertain, this work could open up new applications for solar power in the long term. "We have a proof-of-concept that works," Bulovic noted. The next question is, "How many miracles does it take to make it scalable? We think it's a lot of hard work ahead, but likely no miracles needed."

"This demonstration by the MIT team is almost an order of magnitude thinner and lighter" than the previous record holder, said Max Shtein, an associate professor of materials science and engineering, chemical engineering, and applied physics, at the University of Michigan, who was not involved in this work. As a result, he said, it "has tremendous implications for maximising power-to-weight (important for aerospace applications, for example), and for the ability to simply laminate photovoltaic cells onto existing structures."

"This is very high quality work," Shtein added, with a "creative concept, careful experimental set-up, very well written paper, and lots of good contextual information." And, he said, "The overall recipe is simple enough that I could see scale-up as possible."

The work was supported by Eni S.p.A. via the Eni-MIT Solar Frontiers Centre, and by the National Science Foundation.

- David L. Chandler
  MIT News Office

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