New solar cell is so thin and light it can rest on a bubble

The field of solar energy took a giant leap forward today, as researchers from MIT created the thinnest, lightest solar cells ever made—so light, in fact, that they can rest on a bubble.

As described in the journal Organic Electronics, the team has successfully completed a proof-of-concept test of a new technique for making solar cells—one that could lead to solar cells finding their way to hats, shirts, cell phones, or even simple balloons.

How did they achieve this?

The key, according to MIT associate dean for innovation and co-author Vladimir Bulović, is to cut down on the number of steps needed to make a cell—by making the solar cell, the substrate that supports the cell, and the protective coating that shields the cell from the environment in a single process.

“The innovative step is the realization that you can grow the substrate at the same time as you grow the device,” said Bulović in an MIT statement.

Furthermore, because the substrate is made simultaneously and is never removed from the vacuum chamber where the cell is produced, it has minimal exposure to contaminants like dust—which can lower a solar cell’s performance.

In this particular experiment, the substrate and overcoat were both made from a common flexible polymer known as parylene—which is a commercially available coating used to protect circuit boards from environmental damage. Meanwhile, they used an organic material known as DBP as the primary light-absorbing layer, although the team emphasized that these materials were only some of the potential options—as their in-line substrate manufacturing process is the key aspect here. 

Both the substrate and the solar cell are “grown” using vapor deposition techniques at room temperature—a sharp break from conventional methods, which required both high temperatures and harsh chemicals to make the cell. The parylene film is first deposited on a carrier material—like glass, in this experiment—and after the cell is fabricated, it’s lifted from the carrier using a frame made of flexible film. 

Or, in short: “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 MIT research scientist Annie Wang.

The end result: A solar cell that can rest on a soap bubble without popping it. Interestingly, this might actually be too thin to be practical (“If you breathe too hard, you might blow it away,” said MIT doctoral student Joel Jean)—but it’s a huge step nonetheless. The solar cells are ultra-thin—1/50th the thickness of a human hair—but convert sunlight with one of the highest power-to-weight ratios ever achieved, at about 6 watts per gram.

Which means that these solar panels could be added to just about anything, but especially objects where weight is a huge consideration—like spacecraft.

Of course, there’s still a long way to go from here.

“We have a proof-of-concept that works,” said Bulović. But 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.”


Image credit: Joel Jean and Anna Osherov, MIT