Ceramics in Energy

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ceramics in energy bulletin f i r s t This article first appears exclusively in the Bulletin, and can later be found online on Ceramic Tech Today. Ultrathin, superlight, flexible solar cells could power next-gen portable electronics Researchers at the Massachusetts Institute of Technology have developed a proof-of-concept for “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,” according to an MIT press release. The real deal may be years away from large-scale development, but this new approach to making solar cells could be key in powering the next generation of portable electronic devices, the release explains. MIT professor Vladimir Bulovi´c, research scientist Annie Wang, and doctoral student Joel Jean say the key 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, according to the release. “The innovative step is the realization that you can grow the substrate at the same time as you grow the device,” Bulovi´c says. The single-process approach means the substrate is not handled, cleaned, or removed from the vacuum during fabrication, drastically minimizing any exposure to contaminants that might degrade performance. For the substrate and the overcoating, the team used a common flexible polymer called parylene—a commercially available plastic coating used to protect implanted biomedical devices and printed circuit boards from environmental damage—and an organic material called DBP as the primary light-absorbing layer, the release explains. And, unlike conventional solar cell manufacturing, which requires high temperatures and harsh chemicals, this process takes place in a vacuum chamber at room temperature and sans solvents. “The substrate and the solar cell are ‘grown’ using established vapor deposition techniques,” the release explains. The materials used in this proof-ofconcept were just examples—the in-line substrate manufacturing process is the key innovation, the team emphasizes. “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,” the scientists explain. For the proof-of-concept, the team used a flexible parylene film—only one-tenth as thick as traditional kitchen cling wrap—and deposited it on glass, a more sturdy carrier material. After fabrication, the scientists lifted the entire parylene/solar cell/ parylene stack off the carrier using a frame made of flexible film. The final ultrathin product is just one-fiftieth the thickness of a strand of human hair and one-thousandth the thickness of equivalent cells on glass substrates—which are about two micrometers thick. Yet, “they convert sunlight into electricity just as efficiently as their glass-based counterparts,” says the team. The researchers demonstrated just how thin these thin solar cells are by draping a working cell on top of a soap bubble without popping the bubble. That is impressively thin—but is it too thin to be practical? “Parylene films of thicknesses of up to 80 micrometers can be deposited easily using commercial equipment, without losing the other benefits of in-line substrate formation,” the team says. The time it will take to scale-up this material is still up in the air, but this work could be a new frontier in the solar power revolution. “We have a proof-of-concept that works,” Bulovi´c 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 research, published in Organic Electronics, is “In situ vapor-deposited parylene substrates for ultra-thin, lightweight organic solar cells” (DOI: 10.1016/j.orgel.2016.01.022). n 20 www.ceramics.org | American Ceramic Society Bulletin, Vol. 95, No. 3 Credit: Joel Jean and Anna Osherov; MIT To demonstrate the thinness and lightness of newly developed solar cells, MIT researchers draped a working cell on top of a soap bubble, without popping the bubble.


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