German researchers have found graphene can retain its properties even when coated with silicon.
The team from the Helmholz Research Centre (HZB) in Berlin, Germany, has managed to deposit a layer of graphene on a thin copper sheet and transfer it subsequently to a glass substrate, before coating it with silicon.
When measuring the performance of the final product, the team has found that despite changing its surface structure completely, the miniscule graphene-based solar cells were about 30 times more efficient in transporting charge carriers within the embedded graphene than conventional zinc oxide-based contact layers.
"We examined how graphene's conductive properties change if it is incorporated into a stack of layers similar to a silicon-based thin film solar cell and were surprised to find that these properties actually change very little," said Marc Gluba, a researcher at the HZB Institute for Silicon Photovoltaics.
"That's something we didn't expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon," added Guba’s colleague Norbert Nickel.
Graphene has exceptional conductivity and is completely transparent, inexpensive and nontoxic at the same time, making it a perfect candidate for manufacturing of transparent contact layers for use in solar cells. However, until now, it hasn’t been proven the wonder material can maintain its unparalleled qualities when interacting with other chemical substances.
The Berlin-based team has tested graphene’s interactions with two different types of silicon that are commonly used in conventional silicon thin-film technologies. First of those contains an amorphous silicon layer, in which the silicon atoms are in a disordered state similar to a hardened molten glass. The second sample contained poly-crystalline silicon to help the researchers observe how crystallization processes affect graphene's properties.
"Admittedly, it's been a real challenge connecting this thin contact layer, which is but one atomic layer thick, to external contacts. We still have to work on that," Nickel said. "Our thin film technology colleagues are already pricking up their ears and want to incorporate it."
Although having obtained their measurements on one square centimetre samples, the researchers believe it is feasible to coat much larger areas with graphene.