Common Bug Opens Door To Next-Gen Graphene Solar Cells

August 11th, 2016 by Tina Casey

The Intertubes are buzzing with news about a new method for creating sheets of graphene that possess a new class of electronic properties. The new research has huge implications for the next generation of smaller, lighter, cheaper solar cells and other electronic devices, but that’s not the only thing that’s generating excitement.

Next-Gen Solar Cells With A Bacterial Assist

A good part of the buzz over the new graphene research is due to the unusual fabrication method that it deploys.

The sheets have unique electronic properties because they are formed with nanoscale wrinkles, and the wrinkles are there because the researchers introduced bacteria into the fabrication process.

Yes, bacteria — one of the oldest organisms on Earth — has been deployed to tailor one of science’s newest materials (graphene was discovered in 2004).

The idea of creating wrinkles in graphene sheets is not particularly new, but conventional methods involve stretching a sheet and letting it “snap” back. It’s effective, but the results are not particularly precise.

The team behind the new project is based at the University of Illinois at Chicago. They hit upon the idea of building precise wrinkles directly into graphene by lining up arrays of bacteria.

For this project they used Bacillus subtilis, a much studied soil-dwelling bacteria used in manufacturing antibiotics. It is a tough little number, capable of lying dormant practically forever, so it’s a good prospect for integrating with manufactured products.

Under a microscope, the bacteria look like tiny sausages. The research team got them to line up like rows of sausage strings by exposing them to an electric field under a sheet of graphene.

In the next step, they exposed the graphene/bacteria combo to a vacuum. The vacuum sucks water from the bacteria, forcing them to shrink. Because graphene is relatively flexible, it reconfigures to conform to the shrunken rows of bacteria, et voilà there you go: precisely aligned nanoscale wrinkles.

Atomic force microscopy shows how the graphene sheet looks when draped over the bacteria (left image), and how the wrinkled sheet looks after the vacuum treatment (right image, at 2x magnification):

As described by team leader Vikas Berry, the vacuum process creates carbon nanotubes, so the resulting material is a hybrid with properties that are different from plain graphene:

“The wrinkle opens a ‘V’ in the electron cloud around each carbon atom…” creating a dipole moment, which can open an electronic band gap that flat graphene does not have.

According to Berry, the uniform rows create a differential in the electric field, so that the current running crosswise is less than the current lengthwise.

Next steps for the team include refining and tailoring the wrinkles more precisely, with the goal of making wavelength wrinkles of about two nanometers — the “smallest in the world,” according to Berry.

You can get more details in the journal Nano under the title, “Confined, Oriented, and Electrically Anisotropic Graphene Wrinkles on Bacteria.” For those of you on the go, here’s a snippet from the abstract (anistropic refers to materials that exhibit different properties depending the direction in which they are measured):

…The results obtained show bio-induced production of confined, well-oriented, and electrically anisotropic graphene wrinkles, which can be applied in electronics, bioelectromechanics, and strain patterning.

Making America Great Again…With Bacteria

Bacteria have been inching their way into the clean tech field in many other ways. One favorite subject is cyanobacteria, which a team at Binghampton State University recently harnessed to created a working bio-based solar cell.

At Kansas State University, researchers have also been looking at a bacteria-sourced dye to replace toxic chemicals used in dye-sensitized solar cells. Bacteria have also been emerging in the energy storage field, so stay tuned for that.

In terms of advanced manufacturing, researchers are using bacteria to pry apart the mysteries of biological self-assembly.

When you throw 3-D printing, modular assembly, and robotics into the mix, you’re looking at a future manufacturing landscape that is very different from the traditional human-assisted assembly line.

Images: top (cropped) Bacillus subtillis colonies by Debivort at the English language Wikipedia (creative commons license); bottom via University of Illinois at Chicago.









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