Skip to main content

Solar cells as light as a soap bubble

Ultrathin, flexible photovoltaic cells could find many new uses.

Imagine solar cells so thin, flexible, and lightweight that they could be placed on almost any material or surface, including your hat, shirt, or smartphone, or even on a sheet of paper or a helium balloon.

Researchers at MIT have now demonstrated just such a technology: the thinnest, lightest solar cells ever produced. Though it may take years to develop into a commercial product, the laboratory proof-of-concept shows a new approach to making solar cells that could help power the next generation of portable electronic devices.
The new process is described in a paper by MIT professor Vladimir Bulovic, research scientist Annie Wang, and doctoral student Joel Jean, in the journalOrganic Electronics.
Bulovic, MIT's associate dean for innovation and the Fariborz Maseeh (1990) Professor of Emerging Technology, says the key to the new approach is to make the solar cell, the substrate that supports it, and a protective overcoating to shield it from the environment, all in one process. The substrate is made in place and never needs to be handled, cleaned, or removed from the vacuum during fabrication, thus minimizing exposure to dust or other contaminants that could degrade the cell's performance.




"The innovative step is the realization that you can grow the substrate at the same time as you grow the device," Bulovic says.
In this initial proof-of-concept experiment, the team used a common flexible polymer called perylene as both the substrate and the overcoating, and an organic material called DBP as the primary light-absorbing layer. Parylene is a commercially available plastic coating used widely to protect implanted biomedical devices and printed circuit boards from environmental damage. The entire process takes place in a vacuum chamber at room temperature and without the use of any solvents, unlike conventional solar-cell manufacturing, which requires high temperatures and harsh chemicals. In this case, both the substrate and the solar cell are "grown" using established vapor deposition techniques.
One process, many materials




The team emphasizes that these particular choices of materials were just examples and that it is the in-line substrate manufacturing process that is the key innovation. Different materials could be used for the substrate and encapsulation layers, and different types of thin-film solar cell materials, including quantum dots or perovskites, could be substituted for the organic layers used in initial tests.
But already, the team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble. The researchers acknowledge that this cell may be too thin to be practical -- "If you breathe too hard, you might blow it away," says Jean -- but perylene films of thicknesses of up to 80 microns can be deposited easily using commercial equipment, without losing the other benefits of in-line substrate formation.
A flexible perylene film, similar to kitchen cling-wrap but only one-tenth as thick, is first deposited on a sturdier carrier material -- in this case, glass. Figuring out how to cleanly separate the thin material from the glass was a key challenge, explains Wang, who has spent many years working with perylene.
The researchers lift the entire perylene/solar cell/perylene stack off the carrier after the fabrication process is complete, using a frame made of flexible film. The final ultra-thin, flexible solar cells, including substrate and overcoating, are just one-fiftieth of the thickness of a human hair and one-thousandth of the thickness of equivalent cells on glass substrates -- about two micrometers thick -- yet they convert sunlight into electricity just as efficiently as their glass-based counterparts.
No miracles needed




"We put our carrier in a vacuum system, then we deposit everything else on top of it, and then peel the whole thing off," explains Wang. Bulovic says that like most new inventions, it all sounds very simple -- once it's been done. But actually developing the techniques to make the process work required years of effort.
While they used a glass carrier for their solar cells, Jean says "it could be something else. You could use almost any material," since the processing takes place under such benign conditions. The substrate and solar cell could be deposited directly on fabric or paper, for example.
While the solar cell in this demonstration device is not especially efficient, because of its low weight, its power-to-weight ratio is among the highest ever achieved. That's important for applications where weight is important, such as on spacecraft or on high-altitude helium balloons used for research. Whereas a typical silicon-based solar module, whose weight is dominated by a glass cover, may produce about 15 watts of power per kilogram of weight, the new cells have already demonstrated an output of 6 watts per gram -- about 400 times higher.
"It could be so light that you don't even know it's there, on your shirt or on your notebook," Bulovic says. "These cells could simply be an add-on to existing structures."
Still, this is early, laboratory-scale work, and developing it into a manufacturable product will take time, the team says. Yet while commercial success in the short term may be uncertain, this work could open up new applications for solar power in the long term. "We have a proof-of-concept that works," Bulovic 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."
The work was supported by Eni S.p.A. via the Eni-MIT Solar Frontiers Center, and by the National Science Foundation.
Story Source:
The above post is reprinted from materials provided by Massachusetts Institute of Technology. The original item was written by David L. Chandler. Note: Materials may be edited for content and length.

Comments

Popular posts from this blog

10 URLs to Find Out What Google Knows About You

Google is much more than just a search giant. It is also home to many of your favorite products: Gmail, YouTube, and Chrome, just to name a few. Apart from that, it also offers many products to help you  keep track of your data . Most of these are  hidden deep  inside the My Account dashboard, which many users don’t really know of. These hidden tools  may reveal interesting details  about your usage of Google’s many services. We’ve compiled a list of important Google URLs of some  hidden tools  that carry information of what you did with Google, mostly from the searches that you have made on their many products, the voice searches and typed out Google searches that you have made. Are you ready to  find out what how Google knows about you ? 1.  Google Dashboard Google Dashboard offers  transparency and control over the personal data stored with your Google Account. You can  view  and  manage the data gener...

Edible water balloons that could get rid of the need for plastic bottles

In case you didn’t know, bottled water is destroying the planet. We know that we need to be drinking plenty of water. It’s important. But the plastic bottles they’re sold in are terrible for the environment. One solution is using reusable bottles that you can fill from any nearby taps instead of buying a new bottle each time. Another solution is much more exciting. A group of engineers from Skipping Rocks Lab have developed a wonderful thing called The Ooho!. It’s a globe filled water that you can pop in your mouth whole. The outer shell is made of algae, so it’s edible and biodegradable. Meaning there’s no need for packaging or plastic – the globes of water are self-contained and ready to consume. Exciting, right? Plus they’re wobbly and they look cool, which is always a bonus. The team have now created a crowdfunding page to make their creation available to the public, with goals of selling The Ooho! at festival and marathons within the next 12 m...

New "Super-Earth" discovered only 22 light years away

An international team of scientists led by Professors Guillem Anglada-Escudé and Paul Butler from the Carnegie Institution for Science in the U.S. has discovered a potentially habitable Super-Earth that's "just" 22 light years away. The new Super-Earth has a mass that is 4.5 times larger than that of our planet and it revolves around its parent star in 28 days - a star that is significantly smaller than ours. This remarkable new discovery suggests that habitable planets could exist in a wider variety of environments than previously believed. Of the 750-odd  exoplanets  (extrasolar planets) discovered so far only very few can be considered " Super-Earths ." This newly discovered example called GJ667Cc is rocky like Earth and is rich in heavy chemical elements such as iron, carbon and silicon. Positioned at a distance from Earth of 22 light years, corresponding to a bit over 129 trillion miles (209 trillion km), the planet can be considered to be on Earth...