Researchers from the Brookhaven National Laboratory (BNL) in the United States have turned up an unexpected property of common glass: it makes a good substrate for graphene-based electronics in applications like solar cells and touch-screens.
While graphene has had “wonder-material” status for a few years now, it's difficult to fabricate, because you have to deposit layers of carbon one or two atoms thick.
What the BNL group has found is that a substrate of soda-lime glass – the common type of glass found in bottles and windows – “dopes” the graphene laid on it, creating (for example) an efficient solar cell junction.
Doping is the process of introducing impurities in materials like semiconductors to increase the number of electrons or holes in a material, and it's only useful if the end product doesn't degrade over time. Doping graphene has proven difficult and expensive, and that's why the researchers reckon they've got something important.
As the laboratory explains, the sodium in the glass creates high electron density in the graphene – and the effect can survive “several weeks” exposure to air.
Left: a schematic of the graphene-CIGS-glass layering. Right: scanning-electron micrograph of the junction
Image: Brookhaven National Laboratory
Their original intent was to test a variety of different doping mechanisms. They needed a baseline for those tests, so they started with a stack of graphene on top of a copper-indium-gallium-diselenide semiconductor, with the soda-lime glass as the bottom substrate.
Their surprise came when the baseline tests showed the graphene was “optimally doped” by the glass, without any other chemicals.
According to one of the paper's authors, ex-BNL researcher Nanditha Dissanayake (now of Voxtel): "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 research comes with the usual “more work is needed” caveat, but the point is that a non-exotic substrate and a relatively simple process are the kinds of characteristics that offer a path to scalable and low-cost manufacturing. ®