Solar power has been growing wildly in popularity over the past decade or so, increasing in prevalence by about 40 percent each year. It currently accounts for about 1 percent of the world’s total energy expenditures.
But the technology is still expensive. Even as solar panels themselves have decreased in price, the cost of installation remains high—up to 80 percent of the cost of getting solar panels comes from the installation itself, which involves securing heavy panels to often-sloped surfaces like roofs.
Professor Vladimir Bulović and his MIT colleagues Joel Jean and Annie Wang were interested in dealing with this high installation cost and other problems when they set out to make an ultra-light solar cell.
“If one could make [a solar cell] very lightweight, in principle one could make a very large solar cell that could be unrolled on someone’s roof or in a field,” Bulović says. “Then installation might be as simple as stapling the unrolled panel to the roof.”
Bulović and his team have taken the first step towards this goal. They’ve created a solar cell so light it can literally sit atop a soap bubble without bursting it. It’s only 2.3 microns thick, or 1/30th to 1/50th the thickness of a human hair. It’s so thin it could in theory be used on almost any surface, even incredibly delicate ones—balloons, clothing, paper and human skin.
The team knew the key to the ultra-light solar cell would be in replacing a heavy substrate—the material, usually glass, on which the solar cell layers are formed—with a lighter one. They would also need to use a room temperature process to create the solar cells, as the high temperature process used to create conventional solar cells would melt or damage lighter substrates.
The material the team eventually settled on for the sake of the proof of concept was parylene, a flexible polymer similar to, but much thinner than, Saran wrap. Working atop a slab of glass, they deposited a very thin layer of solar cell material on top of the parylene in a vacuum chamber, then sealed it with another layer of parylene. They then peeled the solar cell sandwich off the glass.
The resulting ultra-light solar cell can generate 6 watts of power per gram, about 400 times more than its conventional counterpart. The new process is detailed in the journal Organic Electronics.
The next step will be to figure out how to manufacture the ultra-light solar cells in larger quantities. The method used to deposit the solar cell material on the substrate is currently quite slow, and will need to be sped up to efficiently produce larger ultra-light solar cells. The team will also need to road test different substrates for strength and durability.
"We should prove that it can steadily operate for a few years, as needed for portable applications," Bulović says.
The ultra-light solar cells could be useful in areas where weight is of utmost importance, such as on space shuttles. They could be used to power ordinary household devices—electronic touch paper, touchpads, sensors—without adding weight and bulk. They could also potentially be combined with another one of Bulović’s innovations—transparent solar cells—to create a nearly invisible source of power on almost any surface.
“Our goal is to reimagine what a solar cell is and reimagine what solar technology can be deployed as,” Bulović says.
The engineer estimates it will take about a decade before his team’s technology becomes mainstream.
“To go from this structure to a bigger one, we can certainly envision what it would take to get there,” he says. “There are not a significant number of unknowns. The tasks ahead should be conquerable.”