Samsung have also shown they can integrate onto the graphene sheets organic light-emitting diodes– the light sources used in most smartphones. What’s more the OLEDs wired up this way are more efficient and brighter than those based on indium-tin-oxide, so they’ll help batteries last longer.
The same kind of science that lets graphene-based devices turn electricity into light allows the reverse to happen. As a result, there’s interest in whether graphene sensors could replace the CCD cameras in your phone. And, perhaps more significantly, there’s interest in whether graphene would make an efficient solar cell. Last year, a team at the University of Florida showed they could achieve 8.6% energy conversion using graphene-based cells – far behind current commercial silicon photovoltaics (which achieve around 20%), but already a factor of four better than earlier than previous attempts. And, as many point out, silicon has been under development for decades, not just a few years.
Part of the reason why researchers are so excited about graphene’s potential in highly efficient solar cells was recently revealed by research done at the European Institute of Photonic Science (ICFO). Working with researchers from the US, Spain and Germany, the team was able to show that the material is able to convert a single light particle into cascades of electrons helping more light energy to be turned into current.
"In most materials, one absorbed photon generates one electron, but in the case of graphene, we have seen that one absorbed photon is able to produce many excited electrons, and therefore generate larger electrical signals," explained Frank Koppens , group leader at ICFO at the time.
Of course, having generated your electricity, you want to capture it.
And new research from the Nokia Research Labs in Cambridge, UK, shows that graphene can help there, too. A team at the labs recently describe the graphene-based rechargeable battery no thicker than a human hair (50 microns) – ideal for building into the case of a future, flexible phone.
The prototype power pack is a lithium ion battery, like most rechargeables used in electronics. These already use graphite to capture the charge from the lithium-ion reactions that generate the battery power. But the belief is that the ultrathin graphene layers can achieve a much closer contact with the lithium ions, to improve performance of the battery. This is achieved because a gram of graphene has a surface area of 2,600 square metres –the equivalent of about ten tennis courts – meaning there are more opportunities for a reaction to occur in the battery.
Currently, the very thinness of the Nokia battery limits how much charge it can hold. But other researchers have developed graphene foams, that are thicker, hold more charge, but are still completely flexible.
The prototype Nokia batteries, like the Samsung screens use graphene layers grown by condensing hot carbon vapour onto thin copper foil. It’s a remarkably successful approach, but energy intensive and relatively expensive. As a result, other researchers have explored another lower-tech approach that seems to produce perfectly good material: graphene ink.
The starting material is plain old graphite that is literally shaken to pieces using ultrasound. The resulting ink is an unexceptional black. But researchers at Cambridge University, UK, have manufactured basic electronic components using this kind of graphene solution and an ordinary office ink-jet printer.
All of these developments could play a part in the flexible future of the mobile industry. But perhaps, where graphene has caused the most excitement is within the chip industry.
For the past 50 years, the industry has been relentlessly driven by Moore’s law – which states that the number of transistors that can be squeezed onto an area of silicon for a fixed price double roughly every 18 months. As a result, silicon firms continually design and manufacture electronic components of ever-shrinking size, the reason more than a billion components can be squeezed onto a chip just a centimetre or two across. But each generation of shrinkage has become harder, and how to keep going beyond the horizon three or four generations away has long been a worry.
The crystalline perfection of graphene combined with its high conductivity in principle seems to hold out the promise of electronics at close to the molecular scale. Also, electronic devices like diodes and transistors had already been made with graphene’s straw-like cousin, carbon nanotubes.
But in practice, graphene doesn’t offer the same degree of electronic control as silicon. You might think of it as like running a formula one race on an ice rink: with electrons able to zip through the carbon lattice at the speed of light, there is little prospect of guiding the current, turning it on and off electronically as is essential in computer chips.
But the allure is so great that a huge amount of research effort has been pushed towards future electronics, particularly at IBM and Samsung. In 2011, IBM triumphantly proclaimed the fabrication of “a wafer-scale graphene circuit … in which all the circuit components … were monolithically integrated.” In plain language they had been able to manufacture useful circuitry at a size and scale normally used in the silicon industry.
The circuit was a so-called broadband radio-frequency mixer, an essential component of TVs, phones and radio but very different from the complex logic chip found at the heart of a smartphone or laptop. The circuit is generally used to convert the high frequency signals broadcast by radio stations to a lower frequency that we can hear.
The circuit exploited the high speed of electrons in graphene, something that may also make graphene ideally suited to handle the high frequencies of mobile phone transmissions – both in the receiver and in generating the signal to send out to the base station.
The IBM researchers have made graphene components that operate up to 150 GHz, well above the frequencies currently used by mobile phones, and in principle opening up new portions of spectrum for cell phone coverage and improving connectivity.
Although the IBM team declared their “results open up possibilities of achieving practical graphene technology with more complex functionality,” in practice, getting the kind of data processing that goes on in silicon chips requires devising transistor circuits that can turn current on and off digitally. Nobel laureate Konstantin Novoselov has argued that despite several promising leads, it could be 2025 before large-scale integration of huge numbers of graphene components will be a reality. But by then, silicon may already have maxed out.
Hype or hope?
The list of potential uses of graphene goes on – as a replacement for the flash memory of our SD cards, or to replace the metal antennae that pick up the radio signal. But one which shows just how varied the material’s properties can be is its use in the earpiece.