Transparent graphene electrodes might lead to new generation of solar cells | MIT News

A brand new approach of creating massive sheets of high-quality, atomically skinny graphene may result in ultra-lightweight, versatile photo voltaic cells, and to new lessons of light-emitting units and different thin-film electronics.

The brand new manufacturing course of, which was developed at MIT and needs to be comparatively straightforward to scale up for industrial manufacturing, includes an intermediate “buffer” layer of fabric that’s key to the approach’s success. The buffer permits the ultrathin graphene sheet, lower than a nanometer (billionth of a meter) thick, to be simply lifted off from its substrate, permitting for fast roll-to-roll manufacturing.

The method is detailed in a paper printed yesterday in Superior Practical Supplies, by MIT postdocs Giovanni Azzellino and Mahdi Tavakoli; professors Jing Kong, Tomas Palacios, and Markus Buehler; and 5 others at MIT.

Discovering a strategy to make skinny, large-area, clear electrodes which can be steady in open air has been a serious quest in thin-film electronics lately, for a wide range of purposes in optoelectronic units — issues that both emit gentle, like pc and smartphone screens, or harvest it, like photo voltaic cells. Right this moment’s customary for such purposes is indium tin oxide (ITO), a cloth based mostly on uncommon and costly chemical components.

Many analysis teams have labored on discovering a alternative for ITO, specializing in each natural and inorganic candidate supplies. Graphene, a type of pure carbon whose atoms are organized in a flat hexagonal array, has extraordinarily good electrical and mechanical properties, but it’s vanishingly skinny, bodily versatile, and created from an considerable, cheap materials. Moreover, it may be simply grown within the type of massive sheets by chemical vapor deposition (CVD), utilizing copper as a seed layer, as Kong’s group has demonstrated. Nevertheless, for system purposes, the trickiest half has been discovering methods to launch the CVD-grown graphene from its native copper substrate.

This launch, often known as graphene switch course of, tends to end in an internet of tears, wrinkles, and defects within the sheets, which disrupts the movie continuity and subsequently drastically reduces their electrical conductivity. However with the brand new know-how, Azzellino says, “now we’re in a position to reliably manufacture large-area graphene sheets, switch them onto no matter substrate we wish, and the way in which we switch them doesn’t have an effect on {the electrical} and mechanical properties of the pristine graphene.”

The bottom line is the buffer layer, made from a polymer materials known as parylene, that conforms on the atomic degree to the graphene sheets on which it’s deployed. Like graphene, parylene is produced by CVD, which simplifies the manufacturing course of and scalability.

As an indication of this know-how, the staff made proof-of-concept photo voltaic cells, adopting a thin-film polymeric photo voltaic cell materials, together with the newly fashioned graphene layer for one of many cell’s two electrodes, and a parylene layer that additionally serves as a tool substrate. They measured an optical transmittance near 90 % for the graphene movie below seen gentle.

The prototyped graphene-based photo voltaic cell improves by roughly 36 instances the delivered energy per weight, in comparison with ITO-based state-of-the-art units. It additionally makes use of 1/200 the quantity of fabric per unit space for the clear electrode. And, there’s a additional elementary benefit in comparison with ITO: “Graphene comes for nearly free,” Azzellino says.

“Extremely-lightweight graphene-based units can pave the way in which to a brand new era of purposes,” he says. “So if you concentrate on moveable units, the facility per weight turns into an important determine of advantage. What if we may deploy a clear photo voltaic cell in your pill that is ready to energy up the pill itself?” Although some additional growth can be wanted, such purposes ought to in the end be possible with this new methodology, he says.

The buffer materials, parylene, is extensively used within the microelectronics business, normally to encapsulate and shield digital units. So the availability chains and tools for utilizing the fabric already are widespread, Azzellino says. Of the three current forms of parylene, the staff’s exams confirmed that considered one of them, which accommodates extra chlorine atoms, was by far the best for this utility.

The atomic proximity of chlorine-rich parylene to the underlying graphene because the layers are sandwiched collectively gives an additional benefit, by providing a form of  “doping” for graphene, lastly offering a extra dependable and nondestructive strategy for conductivity enchancment of large-area graphene, in contrast to many others which were examined and reported thus far.

“The graphene and the parylene movies are all the time face-to-face,” Azzellino says. “So mainly, the doping motion is all the time there, and subsequently the benefit is everlasting.”

The analysis staff additionally included Marek Hempel, Ang-Yu Lu, Francisco Martin-Martinez, Jiayuan Zhao and Jingjie Yeo, all at MIT. The work was supported by Eni SpA via the MIT Power Initiative, the U.S. Military Analysis Workplace via the Institute for Soldier Nanotechnologies, and the Workplace of Naval Analysis.

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