Graphene is often referred to as a kind of wonder material, due to the amazing properties it displays, such as conduction, super-strength, and flexibility, but for all its vaunted wondrousness, there's one area where scientists have been struggling to get the nano-material to perform: the one-atom-thick molecular structure of graphene is inherently poor at trapping light.
Now a team in the UK has figured out how to manipulate the material into what they claim is the most light-absorbent material for its weight to date, which could lead to all kinds of new solar-based technologies in the future.
"As a result of its thinness, graphene is only able to absorb a small percentage of the light that falls on it," said nano-electronics researcher José Anguita from the University of Surrey. "For this reason, it is not suitable for the kinds of optoelectronic technologies our 'smart' future will demand."
To get around this limitation, the researchers took their cues from an unlikely source: moth eyes. By emulating how extremely small texturing on the eyes of moths capture light – which enables them to see in the dark – the researchers have significantly upped graphene's own light-absorption potential.
"Nature has evolved simple yet powerful adaptations, from which we have taken inspiration in order to answer challenges of future technologies," said Ravi Silva, head of the University's Advanced Technology Institute. "Moths' eyes have microscopic patterning that allows them to see in the dimmest conditions. These work by channelling light towards the middle of the eye, with the added benefit of eliminating reflections, which would otherwise alert predators of their location."
Mimicking this with their own kind of nanotexturing, the researchers grew graphene around a textured metallic surface, with the pattern directing extra light, almost like mirrors, into the molecular structure of the film.
"Nanotexturing graphene has the effect of channelling the light into the narrow spaces between nanostructures, thereby enhancing the amount of light absorbed by the material," said Anguita. "It is now possible to observe strong light absorption from even nanometre-thin films. Typically a graphene sheet would have 2–3 percent light absorption. Using this method, our ultrathin coating of nanotextured few-layer graphene absorbs 95 percent of incident light across a broad spectrum, from the UV to the infrared."
The researchers say that their technique, which is described in Science Advances, could enable solar sensors in existing and new kinds of optical devices, generating power from ambient light and heat that we're not currently taking advantage of.
"Solar cells coated with this material would be able to harvest very dim light," said Silva. "Installed indoors, as part of future 'smart wallpaper' or 'smart windows', this material could generate electricity from waste light or heat, powering a numerous array of smart applications. New types of sensors and energy harvesters connected through the Internet of Things would also benefit from this type of coating."
It's obviously early days for the technology, but if the researchers are able to find a commercial partner to develop their nanotextured graphene further, we might be able to turn solar panels from unwieldy outdoor objects into vanishingly small sensors that fit almost anywhere. Exciting stuff.