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TECH FRONT


Prof. Vladimir Bulovic, MIT’s associate dean for innova- tion, said the key to the new approach is to all at once make the solar cell, the substrate that supports it and a protective overcoating to shield it from the environment. 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 con- taminants that could degrade the cell’s performance.


New insights into graphene G


raphene has been a material of interest for many years, but usable applications have been somewhat elusive. The interaction of the material and its envi-


ronment have significant influence on the use of graphene by the semiconductor industry. A new project from the University of Vienna explores how the pitfalls of graphene can be resolved. One of the biggest challenges is controlling how the


material interacts with its environment at the atomic level. Even the interaction between graphene and the substrate (which is necessary because of graphene’s extreme thinness) was only partly understood. But a team of researchers lead by Thomas Pichler, the head of the Electronic Properties of Materials research group at the University of Vienna, has made progress in making graphene-based nanoelectric components usable for semiconductor technology. “We were able to demonstrate a correlation between


To demonstrate just how thin and lightweight the cells are, researchers at MIT placed the cell on top of a soap bubble.


In this initial proof-of-concept experiment, the team


used a common flexible polymer called parylene as both the substrate and the overcoating, and an organic ma- terial 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 estab- lished vapor deposition techniques. 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 en- capsulation 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. However, the researchers acknowledge that the cell


may be too thin to be practical. At this point, breathing too hard could cause it to blow away, they said.


14


charge transfer—the shifting of electrons—and mechanical strain in graphene for the first time,” Pichler said. “This obser- vation could be of major practical significance, as it means that the entirely contactless measurement of internal strain in graphene-based components may be possible in the future.” The team also made strides in controlling the interface


between graphene and traditional semiconductors like ger- manium on the atomic level for the first time. The project also produced extensive samples of elec-


tronically insulated graphene by manipulating the electron- ic structure of the material. “We replaced certain atoms in the graphene substrate with hydrogen or nitrogen atoms and measured the impact of this substitution on the gra- phene,” Pichler explained. Another approach involved a method known as inter-


calation. With this method, wafer-thin layers of potassi- um, lithium or barium are inserted between the graphene and the substrate.


I


Flexible ‘skin’ reduces radar reflection


owa State University engineers developed a new flex- ible, stretchable and tunable “skin” that uses rows of small, liquid-metal devices to cloak an object from the


sharp eyes of radar. By stretching and flexing the polymer skin, it can be tuned to reduce the reflection of a wide range of radar frequencies.


Summer 2016


Photo courtesy MIT


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