Ultrathin fabric solar cells can turn any surface into a power source
Researchers at MIT say they have developed ultralight fabric solar cells that can quickly and easily turn any surface into a power source. Unlike traditional silicon solar cells, which are fragile and must be encased in glass and packaged in heavy and thick aluminum framing, the durable, flexible solar cells, which are much thinner than a human hair, are glued to a strong, lightweight fabric, making them easy to install on a 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. They are one-hundredth the weight of conventional solar panels, generate 18 times more power-per-kilogram, and are made from semiconducting inks using printing processes that can be scaled in the future to large-area manufacturing.
Because they are so thin and lightweight, say the researchers, the solar cells can be laminated onto many different surfaces, such as onto the sails of a boat to provide power while at sea, adhered onto tents and tarps that are deployed in disaster recovery operations, or applied onto the wings of drones to extend their flying range. The lightweight solar technology can be easily integrated into built environments with minimal installation needs.
“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,” says Vladimir Bulovic, the Fariborz Maseeh Chair in Emerging Technology, leader of the Organic and Nanostructured Electronics Laboratory (ONE Lab), director of MIT.nano, and senior author of a new paper describing the work. “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.”
To produce the solar cells, the researchers used nanomaterials that are in the form of a printable electronic inks. Working in the MIT.nano clean room, they coated 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. However, 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 researchers 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.
The ideal material, say the researchers, was a composite fabric that weighs only 13 grams per square meter, commercially known as Dyneema. This fabric is made of fibers that are so strong they were used as ropes to lift the sunken cruise ship Costa Concordia from the bottom of the Mediterranean Sea. By adding a layer of UV-curable glue, which is only a few microns thick, the researchers adhered the solar modules to sheets of this fabric, forming an ultra-light and mechanically robust solar structure.
“While it might appear simpler to just print the solar cells directly on the fabric,” says Mayuran Saravanapavanantham, an electrical engineering and computer science graduate student at MIT, “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.”
When they tested the device, the 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, which is about 18 times more power-per-kilogram than conventional solar cells.
“A typical rooftop solar installation in Massachusetts is about 8,000 watts,” says Saravanapavanantham. “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 researchers also tested the durability of their devices and found that, even after rolling and unrolling a fabric solar panel more than 500 times, the cells still retained more than 90 percent of their initial power generation capabilities. While the solar cells are far lighter and much more flexible than traditional cells, say the researchers, 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,” says Jeremiah Mwaura, a research scientist in the MIT Research Laboratory of Electronics, “so the team is currently developing ultrathin packaging solutions that would only fractionally increase the weight of the present ultralight devices.”
“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,” says Mwaura. “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.”
For more, see “Printed Organic Photovoltaic Modules on Transferable Ultra-thin Substrates as Additive Power Sources.”
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