Watt's New in Wearables?

The market for wearable electronic devices is booming, thanks to recent advances in processing and sensing technologies. This has made it possible to develop tiny, yet powerful, devices that are comfortable and practical to wear all day long. However, despite the progress that has been made, present wearable devices have a major Achilles’ heel — delivering sufficient energy for operation without adding bulky and obtrusive components, like large, rigid batteries, that make them uncomfortable to use for long periods of time.

With electronic components growing more energy-efficient over time, the opportunity to explore alternative means of providing power has arisen. Many efforts have been undertaken to develop energy harvesting systems that convert the body’s mechanical motions, or differences in temperature, into electrical energy, for example. These systems have been met with varying levels of success, but to date, they are rarely found in commercial products, so the search for alternative power sources continues in earnest.

Solar power is another option that comes to most people’s minds almost immediately when thinking about alternative sources of energy. And there is a lot of potential for solar cells to power wearables. After all, many commercial products are already powered by solar energy. But when it comes to wearables, existing solar technologies have a significant limitation. Given present technologies, high electrical performance and mechanical elasticity are at odds with one another. In other words, if you want to produce a lot of power, the solar cell is going to have to be as stiff as a board.

This problem may soon be a thing of the past, however, thanks to the work of a team of researchers at the Korea Advanced Institute of Science & Technology. They have developed a stretchable, organic solar cell that can be significantly deformed — perfect for on-body use — yet it can also very efficiently convert solar energy into electrical energy to power our devices.

The team’s innovation is centered on a manufacturing technique that allows for a stretchable polymer to be conjugated with a highly electrically conductive polymer through chemical bonding. The conductive polymer is also an invention of the researchers. Not only is it ten times more stretchable than existing technologies, but it also boasts a very impressive photovoltaic conversion efficiency of 19%. That efficiency is comparable to some of the best solar cells in production today.

The flexibility of the organic solar cell enables it to conform to the natural contours of the body, while the stretchability — it can be stretched an additional 40% of its length without damage — allow it to move comfortably with the wearer.

However, despite the obvious utility of these flexible solar cells, there are still limitations on how much energy they can produce. They certainly cannot even begin to rival the energy density of a battery. Moreover, if there is no light source for them to convert to electricity, the device will be unable to operate — at least without a backup battery, which sort of defeats the purpose. But for certain applications, at least, stretchable solar cells could be a game changer.