Pitt’s Tiny Technologies Could Make Big Impact In Solar Industry And Beyond

Jun 28, 2016

Researchers at the University of Pittsburgh are making tiny strides -- no, really -- that could revolutionize the solar industry.

Paul Leu runs a lab at the university where students work with tiny particles called nanotubes.

“Just to give you the idea of the scale of things, if you take one of these nanotubes and you were to enlarge it to the typical circumference of a pillar in a building, and then you take that column and enlarge it by the same scale, that original column would be the size of the diameter of the entire Earth,” Leu said. “So these things are incredibly, incredibly small.” 

They're smaller than the wavelength of visible light.

First-year graduate student Brad Pafchek is trying to create a product that will absorb as much light as possible. He works with a standard silicon disc that looks like a mirror and then exposes it to a plasma or ionized gas.

“This plasma has a bunch of ions and radicals that are flying around at high energy and they etch into the surface,” Pafcheck said. 

That etching creates a surface that, to the eye, has a flat black appearance but, under an electron microscope, resembles conical structures.

“So these bed of needles create kind of like a buffer region that allows light to get absorbed into the silicon itself, which is fantastic for solar cell applications, because that is the whole point to absorb light and create energy,” Pafcheck said.

Pafchek creates this by changing a slew of variables, including the flow rate of the multiple gases used to make the plasma and the power at which they are introduced. 

Those tiny advances might have applications beyond solar energy.

Third-year Ph.D. student Imrul Kayes is creating an antibacterial surface spiked with nanocones. According to Kayes, nearly 300 million structures fill just one square inch of material.

Viewed under an electron microscope, it looks like a bed of nails, but those nails are just 60 nanometers at the tip. By comparison, a red blood cell is about 8,000 nanometers in diameter -- the wavelength of red light is 700 nanometers.  

Kayes coats the silicon spikes with a few nanometers of silver, then exposes it to a common bacteria known to cause serious infections among hospital patients.  

“We have got some results, and it has shown that with the structures… after one (to) three hours, all of the bacteria cells were killed,” Kayes said.

In the same small office, Ph.D. student Tongchuan Gao is creating a conductive metal mesh so fine it’s highly transparent. Such mesh overlays may be used in touch screens and solar cells. Most of the commercially available meshes are made from the rare earth metal Indium, but Gao’s is made of copper.

“Because copper is really inexpensive, and it is really conductive,” Gao said. “By making the copper into this hexagonal nanomesh shape, it can have really good flexibility and really good transparency, because most of the structure is made up of air, just holes.”

Gao said that even after being flexed 1,000 times, the structure shows very little decay. He said that’s key to creating the next generation electronics, including wearable devices and flexible solar cells. 

Leu meets with his students a few times a week in an effort to keep them on track as they test their hypotheses and work through all of the variables.

“One of the important things is you need to be very passionate about it, because it can, for a lot of graduate students, be a very frustrating process,” Leu said. “You try something and it doesn’t work, you try something and it doesn’t work. So you have to really enjoy it a lot and be passionate about it and also be persistent about things.”

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*UPDATED: This story was updated at 11:37 a.m. on Wednesday, June 29, 2016 to clarify technicalities in Gao's and Pafcheck's research.