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Glass substrate could boost electronics potential of graphene

13 February 2016

Scientists have developed a simple and powerful method for creating resilient, customised, and high-performing graphene: layering it on top of common glass.

For an explanation of this image see foot of article (image: Brookhaven National Laboratory)

This scalable and inexpensive process helps pave the way for a new class of microelectronic and optoelectronic devices, from efficient solar cells to touch screens.

The work, led by scientists at the US Department of Energy's Brookhaven National Laboratory, Stony Brook University (SBU), and the Colleges of Nanoscale Science and Engineering at SUNY Polytechnic Institute, could significantly advance the development of truly scalable graphene technologies.

The scientists built the proof-of-concept graphene devices on substrates made of common soda-lime glass. Serendipitously, the sodium atoms in the glass had a powerful effect on the electronic properties of the graphene.

"The sodium inside the soda-lime glass creates high electron density in the graphene, which is essential to many processes and has been challenging to achieve," says co-researcher Nanditha Dissanayake of Voxtel (formerly with the Brookhaven Lab). "We actually discovered this efficient and robust solution during the pursuit of something a bit more complex. Such surprises are part of the beauty of science."

Crucially, the effect remained strong even when the devices were exposed to air for several weeks - a clear improvement over competing techniques. For successful real-world devices, it is important that the local number of electrons transferred to the graphene does not degrade over time.

The team initially set out to optimise a solar cell containing graphene stacked on a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn was stacked on an industrial soda-lime glass substrate. They then conducted preliminary tests of the novel system to provide a baseline for testing the effects of subsequent doping. But these tests showed that the graphene was already optimally doped without the introduction of any additional chemicals.

"To our surprise, the graphene and CIGS layers already formed a good solar cell junction!" says Dissanayake. "After much investigation, and the later isolation of graphene on the glass, we discovered that the sodium in the substrate automatically created high electron density within our multi-layered graphene."

The scientists now need to probe more deeply into the fundamentals of the doping mechanism and more carefully study material's resilience during exposure to real-world operating conditions. The initial results, however, suggest that the glass-graphene method is much more resistant to degradation than many other doping techniques.

Key to the illustration
Left: This is a schematic of a graphene field-effect-transistor used in this study. The device consists of a solar cell containing graphene stacked on top of a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn is stacked on an industrial substrate (either soda-lime glass, SLG, or sodium-free borosilicate glass, BSG).

The research revealed that the SLG substrate serves as a source of sodium doping, and improved device performance in a way not seen in the sodium-free substrate. Right: A scanning electron micrograph of the device as seen from above, with the white scale bar measuring 10 microns, and a transmission electron micrograph inset of the CIGS/graphene interface where the white scale bar measures 100 nanometres.

An article describing this work is published in the journal, Scientific Reports.

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