Reinventing the Solar Cell

This isn't the first time that someone has tried to make solar cells that are thinner and lighter than those currently on the market.

There are the Kirigami-inspired, sun-tracking solar cells from the University of Michigan. There's also the printable solar cell from Australia that's just the size of a piece of paper. And, of course, there are the U.S. Military-developed solar cells that are only a few hundred nanometers thick or 1,000 times thinner than a sheet of paper.

But none of them can compare to the near-invisible solar cell currently being developed by a group of MIT researchers, which is so thin and lightweight, it can be placed on top of a soap bubble without popping it.

Image of the lightweight, flexible solar cell placed on a soap bubble. Credit: Joel Jean and Anna Osherov/MIT News
How Are the Thinnest Solar Cells in the World Made?

According to Vladimir Bulović, MIT’s associate dean for innovation and the Fariborz Maseeh (1990) Professor of Emerging Technology, what sets their solar cells apart is the innovative step of realizing that it's possible to grow the substrate at the same time as the device. Simply put, the trick is to make the solar cell and the protective overcoating all in one process.

Together with research scientist Annie Wang, and doctoral student Joel Jean, the team used a flexible polymer called parylene as both the substrate and the overcoating, and an organic substance called DBP, which is frequently used in organic solar cells, as the light-absorbing material in their initial proof-of-concept experiment.

To create the solar cells, vapor deposition techniques are used to "grow" both the substrate and the solar cell in a vacuum chamber at room temperature.

“We put our carrier in a vacuum system, then we deposit everything else on top of it, and then peel the whole thing off,” says Wang.

The resulting solar cells, which are proven to effectively convert sunlight into electricity just as efficiently as glass-based solar cells, are just one-fiftieth the thickness of a human hair. To underscore the lightness and delicacy of the new cell, the researchers deposited it atop a soap bubble—and did so without popping it.

What Are its Possible Applications?

“It could be so light that you don’t even know it’s there, on your shirt or on your notebook,” says Bulović. “These cells could simply be an add-on to existing structures.”

The ultra-thin solar cells have an output of 6 watts per gram or about 400 times higher than the typical silicon-based solar module. Which is good news for aerospace research where the power-to-weight ratio in solar cells is important.

It could also change the way electronic gadgets such as smartphones, tablets, and laptops are built. Imagine your devices never having to run out of juice, simply by letting them get a bit of sun.

It could also open up new frontiers in the "Internet of Things"—essentially innervating common products and devices with Internet connectivity—by supplying objects with a lightweight, unobtrusive power source.  Think of "smart" clothing, paper, just about anything, implanted with tiny photovoltaic cells and circuitry to provide them with power and connect them to the Web.

These solar cells are still in the early stages of laboratory-scale work, but if successfully produced it could open up new applications for solar power technology.

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