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Phosphorene paves way for ultrathin solar cells, LEDs

Posted: 22 Jul 2015     Print Version  Bookmark and Share

Keywords:graphene  phosphorene  silicon  solar cell  LED 

It may not be too long before we have ultrathin and ultralight solar cells and LEDs, thanks to researchers at the Australian National University (ANU) who have uncovered unique properties from thin layers of phosphorus.

The team used sticky tape to create single-atom thick layers, termed phosphorene, in the same simple way as the Nobel-prize winning discovery of graphene.

Unlike graphene, phosphorene is a semiconductor, like silicon, which is the basis of current electronics technology.

"Because phosphorene is so thin and light, it creates possibilities for making lots of interesting devices, such as LEDs or solar cells," said lead researcher Dr Yuerui (Larry) Lu, from ANU College of Engineering and Computer Science. "It shows very promising light emission properties."


Making phosphorene (Source: Stuart Hay/ANU)

The team created phosphorene by repeatedly using sticky tape to peel thinner and thinner layers of crystals from the black crystalline form of phosphorus.

As well as creating much thinner and lighter semiconductors than silicon, phosphorene has light emission properties that vary widely with the thickness of the layers, which enables much more flexibility for manufacturing.

"This property has never been reported before in any other material," said Lu, whose study is published in the Nature serial journal Light: Science and Applications. "By changing the number of layers we can tightly control the band gap, which determines the material's properties, such as the colour of LED it would make."

"You can see quite clearly under the microscope the different colours of the sample, which tells you how many layers are there," said Lu.

Lu's team found the optical gap for monolayer phosphorene was 1.75 electron volts, corresponding to red light of a wavelength of 700nm. As more layers were added, the optical gap decreased. For instance, for five layers, the optical gap value was 0.8 electron volts, an infrared wavelength of 1,550nm. For very thick layers, the value was around 0.3 electron volts, a mid-infrared wavelength of around 3.5µ.

The behaviour of phosphorene in thin layers is superior to silicon, said Lu. "Phosphorene's surface states are minimised, unlike silicon, whose surface states are serious and prevent it being used in such a thin state."

- Paul Buckley
  EE Times Europe

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