LAWRENCE — Imagine a sheet of chicken wire only one carbon atom thick, and you have a good idea of graphene. The material is the focus of intense research across the world because of its unique properties of electrical conductivity, flexibility, optical transmittance and chemical inertness. Scientists who showed how to make graphene with ordinary Scotch tape recently scored the Nobel Prize in Physics.
Judy Wu, Distinguished Professor of Physics and Astronomy at the University of Kansas, believes graphene will lead to high-efficiency, ultrathin solar panels that will be cheaper to build than current models.
Now, Wu’s research group in KU physics, in collaboration with Professor Rongqing Hui’s group in KU electrical engineering and computer science, has made a breakthrough with the material. They’ve developed a technique for attaching a layer of metal nanoparticles to graphene, vastly improving graphene’s capacity to soak up sunlight and re-emit it in a much-condensed form due to “plasmonic resonance,” a critical step toward high-efficiency solar cells that drastically improves their light absorption.
“We made it in a very simple way, heating a very thin layer of silver on graphene, which dissolves to create a nanoparticle array,” Wu said. ”It’s so straightforward, you can readily commercialize it. It’s very low-cost. “
Wu’s findings are published in the current issue of the journal Advanced Materials, a top-notch international journal in materials research, and also featured on the cover of the March issue of Advanced Optical Materials, which is the journal’s quarterly forum for the publication of the best work in the field of materials science dealing with all aspects of light-matter interactions.
Wu’s technique to make “plasmonic” graphene further boosts the material’s great potential to revolutionize optoelectronics of all kinds.
“At the interface of metal and graphene, a stream of electrons is injected into the graphene, which can enhance its conductivity by 400 percent,“ the KU researcher said. “Also, the metal nanoparticles improve graphene’s ability to absorb and re-emit light.”
Aside from improving performance, Wu’s plasmonic graphene has the potential to make solar cells much cheaper to produce and purchase.
“For solar cells and most optoelectronic applications, you want to use less material,” said Wu. “But current solar cells use a lot of material — 40 percent of solar cell’s cost is material. So if you want to reduce costs, you can immediately reduce the cost of material — and now you can go thinner. Imagine solar cells as thin as a piece of paper, flexible and lightweight.”
Beyond applications in solar-power generation, Wu sees graphene as a promising replacement for indium tin oxide, or ITO, in transparent conductors that are critical to all touchscreens, displays and LEDs.
“Long-term use of ITO has severe limitations,” said Wu. “Indium is scarce and consequently becomes prohibitively expensive as demand for solar cells increases. It was $600-800 per kilogram recently.”
Wu’s group now is exploring ultrathin solar cells on plasmonic graphene and use of plasmonic graphene in photodetectors.
This research was jointly funded by ARO, NSF and the NSF EPSCoR Kansas Center for Solar Energy Research. Wu collaborated on the work with KU researchers Guowei Xu, Jianwei Liu, Qian Wang, Rongqing Hui, and with researchers Zhijun Chen and Victor A. Maroni from Argonne National Laboratory.