Researchers at MIT have created ultra thin, flexible solar cells that can be printed using semiconductor inks and scalable fabrication techniques. They are much thinner than a human hair, weigh 1% as much as a conventional solar panels, and generate 18 times more power per kilogram, according to an MIT blog post.
When glued to a strong, lightweight fabric, they are easy to install on any fixed surface. They can provide energy on the go as a wearable power fabric or be transported and rapidly deployed in remote locations for assistance in emergencies. Because they are so thin and lightweight, these solar cells can be laminated onto many different surfaces, from the sails of a boat to tents and tarps that are deployed in disaster recovery operations. They could even be used to circumnavigate Australia. This lightweight solar technology can be easily integrated into built environments with minimal installation needs, the researchers claim.
“The metrics used to evaluate a new solar cell technology are typically limited to their power conversion efficiency and their cost in dollars per watt. Just as important is integrability — the ease with which the new technology can be adapted. The lightweight solar fabrics enable integrability, providing impetus for the current work. We strive to accelerate solar adoption, given the present urgent need to deploy new carbon-free sources of energy,” says Vladimir Bulović, head of emerging technology at MIT and leader of the Organic and Nanostructured Electronics Laboratory (ONE Lab). He is also the director of MIT.nano, and senior author of a new paper describing this breakthrough work on ultra thin solar cells
His co-authors are Mayuran Saravanapavanantham, an electrical engineering and computer science graduate student at MIT, and Jeremiah Mwaura, a research scientist in the MIT Research Laboratory of Electronics. For readers who wish to delve more deeply into the technical details of this discovery, you can find more — much more — at Small Methods, which published the research paper on December 9. Thankfully, the paper is not behind a paywall and is accessible to anyone with an internet connection.
The Road To Ultra Thin Solar Cells
Traditional silicon solar cells are fragile, which means they have to be encased in glass and packaged in thick aluminum framing. That makes them heavy and inflexible, which in turn limits where and how they can be deployed.
The quest for printed solar cells began over a decade ago. Six years ago, the ONE Lab team at MIT produced solar cells using an emerging class of thin film materials that were so lightweight they could sit on top of a soap bubble. But these ultrathin solar cells were fabricated using complex, vacuum-based processes, which can be expensive and challenging to scale up.
To produce these new ultra thin, flexible solar cells, nanomaterials are used that are in the form of printable electronic inks. Working in the MIT.nano clean room, the researchers coat the solar cell structure using a slot-die coater which deposits layers of the electronic materials onto a prepared, releasable substrate that is only 3 microns thick. Using screen printing (a technique similar to how designs are added to silkscreened T-shirts), an electrode is deposited on the structure to complete the solar module. The researchers can then peel the printed module, which is about 15 microns in thickness, off the plastic substrate, forming an ultralight solar device.
Such thin, freestanding solar modules are challenging to handle and can easily tear, which would make them difficult to deploy. To solve this challenge, the MIT team searched for a lightweight, flexible, and high strength substrate they could adhere the solar cells to. They identified fabrics as the optimal solution, as they provide mechanical resilience and flexibility with little added weight.
They found an ideal material — a composite fabric that weighs only 13 grams per square meter known commercially as Dyneema. This fabric is made of fibers that are so strong they were used as ropes to lift the cruise ship Costa Concordia from the bottom of the Mediterranean (after its captain steered it too close to shore to wave to family and friends, whereupon it hit a rock and sank). By adding a layer of UV-curable glue only a few microns thick, they adhere the solar modules to sheets of that fabric. This forms an ultra-light and mechanically robust solar structure.
“While it might appear simpler to just print the solar cells directly on the fabric, this would limit the selection of possible fabrics or other receiving surfaces to the ones that are chemically and thermally compatible with all the processing steps needed to make the devices. Our approach decouples the solar cell manufacturing from its final integration,” Saravanapavanantham explains.
Outshining Conventional Solar Panels
When they tested the device, the MIT researchers found it could generate 730 watts of power per kilogram when freestanding and about 370 watts per kilogram if deployed on the 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 that same amount of power, our fabric photovoltaics would only add about 20 kilograms (44 pounds) to the roof of a house,” the co-author explains. When tested for durability, the ultra thin solar cells retained more than 90% of their initial power generation capabilities after being rolled and unrolled more than 500 times.
While the MIT solar cells are far lighter and more flexible than traditional cells, they would need to be encased in another material to protect them from the environment. The carbon-based organic material used to make the cells could be modified by interacting with moisture and oxygen in the air, which could deteriorate their performance.
“Encasing these solar cells in heavy glass, as is standard with the traditional silicon solar cells, would minimize the value of the present advancement, so the team is currently developing ultrathin packaging solutions that would only fractionally increase the weight of the present ultralight devices,” says Mwaura.
“We are working to remove as much of the non-solar active material as possible while still retaining the form factor and performance of these ultralight and flexible solar structures. For example, we know the manufacturing process can be further streamlined by printing the releasable substrates, equivalent to the process we use to fabricate the other layers in our device. This would accelerate the translation of this technology to the market,” he adds.
We know that “transition to market” part is often the most difficult part. A review of the CleanTechnica library reveals two stories about printed solar cells by companies that have never been heard from since — one in 2009 and another in 2016. As Tom Petty once told us, “The waiting is the hardest part.”
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