Solar cells are a great way of collecting and storing energy to power gadgets. There's just one problem: they're heavy. A typical silicon-based solar module can only produce about 15 watts of power per kilogram of weight. That's just too heavy to be used in most gadgets, especially mobile devices like smartphones and wearables that could otherwise easily benefit from powering themselves through solar power.
A new innovation from MIT could change that. A team of researchers overseen by MIT professor Vladimir Bulović have figured out how to create flexible solar cells that are around 400 times lighter—so light enough you could add them to nearly any material and not change its behavior or performance. You might even forget they're there.
Most solar cells are made of three distinct parts. You've got the solar cell, which absorbs light, the substrate onto which it is applied, and a protective overcoating to help shield it from its environment. It's this protective coating, usually made from glass, which is responsible for most of the weight of a solar cell. And since these three elements need to be manufactured separately then sandwiched together, producing working solar cells has a lot of potential points of failure which drive up costs: for example, getting dust between the protective outer coating and the solar cell.
Bulović's team, however, has proven that it's possible to "grow" the solar cell, its substrate, and the protective overcoating in a single process—and from most of the same materials. In their proof-of-concept experiment, they used a common flexible polymer called parylene for the substrate and protective coating, and an organic material called DBP for the solar cell. They then "grew" all of these layers, one atop the other, using a process called chemical vapor deposition. The resulting solar cell is so light, it can be laid on a soap bubble without popping it. Despite this, though, it produces an incredible six watts of electricity per gram, all while keeping production costs lower by minimizing the possible points of failure in the creation of a solar cell.
It's this latter aspect that gets photovoltaic nerds like Bulović excited. "The innovative step is the realization that you can grow the substrate at the same time as you grow the device," he told MIT News. But he also admits that the technology is perfect for creating solar cells light enough to power wearables and other portable electronic devices. "It could be so light that you don’t even know it’s there, on your shirt or on your notebook," he says.
That said, Bulović's lightweight solar cells are still just laboratory proof-of-concepts. It'll take considerable money, effort, and time to manufacture at scale. But Bulović says it's doable. "We have a proof-of-concept that works," Bulović says. "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." Soon, everything from your smartphone to the brim of your hat could soon be slathered with solar cells so light, you don't even know they're there.