October R&D Round Up

E-mail Melanie Martella

This month we have electronics that melt away when immersed in a fluid and solar cells that use carbon rather than silicon or polymers to convert light to energy.

It's Melting!
Uncountable man hours and money have gone into developing and building electronics that can withstand pretty much whatever we throw at them, whether that's being sent into space, buried in the middle of a car engine, implanted in a person, or built into a toy that can withstand the attentions of a vigorous small child. There are times, however, where what we most need is something that is not built for the long haul, that's designed to be short-lived and disposable and until recently, that category did not include electronics. The September 28 issue of Science includes a paper describing the materials and processes used to create transient silicon-based electronics that can dissolve when immersed in a fluid. Liz Ahlberg's news article, "Next up: Environmentally safe electronics that also vanish in the body" describes the technology and its potential uses. The multidisciplinary team from the University of Illinois, Tufts University, and Northwestern, have created the devices by adding magnesium electrodes and interconnects and magnesium oxide gate and interlayer dielectrics on top of a very thin silicon layer and then encapsulating the whole thing in a layer of silk. The silicon, magnesium, and magnesium oxide elements will all naturally dissolve in fluids and are biocompatible. By controlling the thickness of the silk encapsulation, the researchers can control how quickly the device will dissolve. As Alberg's article explains, the most attractive applications for the technology are in medical implants, environmental monitoring, and compostable electronics for consumer goods. So clever!

Renewable Energy from Carbon?
Although the photovoltaic cells currently available have greatly improved their ability to convert light to energy, they're still not terribly efficient. Which explains all the research into developing better ones, whether they're improving the solar cells made from monocrystalline silicon wafers or the easier-to-manufacture dye-sensitized solar cells. Now researchers at the University of Kansas have developed solar cells that use carbon nanomaterials to provide the photovoltaic functionality. On the upside, we're never going to run out of carbon and the cells described in "Research yields promising breakthrough in solar cells based on nanocarbon" could share the positive aspects of polymer-based solar cells, namely chemical tunability, the ability to process the components in solution, and potential flexibility but add carbon's photostability. The current downside, however, is that the carbon-based solar cells—that use fullerene, carbon nanotubes, and graphite—have a power efficiency of 1.3% compared to 17%–22% for silicon-based solar cells. So, there's a lot of room for improvement. (I'll also add that I will be interested to see whether this use of carbon nanomaterials pays off as a sensor technology before its use for energy production.)