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MIT researchers have created ultra-thin, flexible solar cells that can be printed using semiconductor inks and scalable manufacturing techniques. They’re thinner than a human hair, 1% heavier than conventional solar panels, and produce 18 times more energy per kilogram, according to an MIT blog post.
Attached to a strong, lightweight fabric, it is easy to mount on any stable surface. They can provide power on the road as portable power supplies or be transported and rapidly deployed to remote locations for emergency assistance. Because they are so thin and light, these solar cells can be laminated to many different surfaces, from boat sails to tents and tarps used in disaster recovery operations. They could even be used to travel around Australia. The researchers claim that this lightweight solar technology can be easily integrated into built environments with minimal installation needs.
“Measurements used to evaluate new solar cell technology are typically limited to their energy conversion efficiency and their cost in dollars per watt. Equally important is integrability—the ease with which new technology can be adapted. Lightweight solar panels provide integration that drives current work. says Vladimir Bulovich, head of MIT’s emerging technology and Laboratory of Organic and Nanostructured Electronics (ONE Lab). He is also the director of MIT.nano and senior author of a new paper describing this breakthrough work on ultrathin solar cells.
Its co-authors are Mayuran Saravanapavanantham, a graduate student in electrical engineering and computer science at MIT, and Jeremiah Mwaura, a research scientist at MIT’s Electronics Research Laboratory. For readers who want to delve deeper into the technical details of this discovery, you can find more in Small Methods, which published a research paper on December 9. anyone with an internet connection.
The road to ultra-thin solar cells
Traditional silicon solar cells are fragile, which means they must be encased in glass and encased in a thick aluminum frame. This makes them heavy and inflexible, which in turn limits where and how they can be placed.
The search for printed solar cells began more than a decade ago. Six years ago, the ONE Lab team at MIT produced solar cells using thin-film materials that were light enough to sit on a soap bubble. But these ultrathin solar cells are made using complex, vacuum-based processes, which can be expensive and difficult to scale up.
Nanomaterials in the form of printable electronic inks are used to produce these new ultra-thin, flexible solar cells. Working in the MIT.nano cleanroom, researchers coat the solar cell structure using a slot-die coating that deposits layers of electronic materials onto a release substrate made just 3 microns thick. Using screen printing (a technique similar to adding designs to silk-screened shirts), an electrode is placed on the structure to complete the solar module. The researchers can then create an ultralight solar device by extruding a printed module about 15 microns thick from a plastic substrate.
Such thin, self-contained solar modules are difficult to handle and can easily tear, making them difficult to deploy. To solve this problem, the MIT team looked for a light, flexible and high-strength substrate to which they could attach solar cells. They identified fabrics as the optimal solution because they provide mechanical stability and flexibility with little added weight.
They found the ideal material—a composite fabric known commercially as Dyneema that weighs just 13 grams per square meter. This fabric is made of fibers so strong that they were used as a rope to raise the Costa Concordia cruise ship from the bottom of the Mediterranean Sea (it hit a rock and sank after the captain brought it too close to shore to wave to family and friends). They attach the solar modules to those fabric layers by adding a layer of UV-curable adhesive just a few microns thick. This creates an ultra-lightweight and mechanically robust solar structure.
“While it may seem simpler to print solar cells directly onto fabric, this would limit the choice of possible fabrics or other receptive surfaces to those that are chemically and thermally compatible with all the processing steps needed to make the devices. Our approach decouples the manufacturing of the solar cell from its final integration,” explains Saravanapavanantham.
Unusual Solar Panels
MIT researchers testing the device found that it can generate 730 watts per kilogram freestanding, and about 370 watts per kilogram when placed on high-strength Dyneema fabric. That’s about 18 times more than conventional solar cells on a power-per-kilogram basis.
“A typical rooftop solar installation in Massachusetts is about 8,000 watts. To generate the same amount of energy, our fabric photovoltaics would add only 20 kilograms (44 pounds) to the roof of a house,” explains the co-author. When tested for durability, the ultra-thin solar cells retained more than 90% of their original power generation capacity after being rolled and unrolled more than 500 times.
Although MIT’s solar cells are lighter and more flexible than traditional cells, they must be surrounded by another material to protect them from the environment. The carbon-based organic material used to make the cells can be altered by interacting with moisture and oxygen in the air, which can degrade their performance.
“Encasing these solar cells with heavy glass, as is standard with traditional silicon solar cells, will minimize the cost of current development, so the team is currently developing ultra-thin packaging solutions that will only slightly increase the weight of existing ultralight devices. ” says Mwaura.
“We are working to remove as much non-solar active material as possible while maintaining the form factor and performance of these ultra-lightweight and flexible solar structures. For example, we know that the manufacturing process can be further simplified by printing releasable substrates, which is equivalent to the process we use to make other layers in our device. This will accelerate the translation of this technology to the market,” he adds.
We know that the “go to market” part is often the hardest part. A review of CleanTechnica’s library reveals two never-before-seen stories about printed solar cells by companies — one in 2009 and the other in 2016. As Tom Petty once told us, “The waiting is the hardest part.”
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