Nanowire organisation method could mean cheaper screens

Duke University chemist Ben Wiley and his graduate student have developed a technique to organise copper atoms to form long, thin, non-clumped nanowires.

The nanowires are then transformed into transparent, conductive films and coated onto glass or plastic for applications in displays on mobile phones, e-readers and iPads. They could also be utilised to build foldable electronics and improved solar cells, according to new research.

According to Duke University, the research shows that the copper nanowire films have the same properties as those currently used in electronic devices and solar cells, but are less expensive to manufacture.

The films that currently connect pixels in electronic screens are made of indium tin oxide (ITO). It is highly transparent, which transmits the information well. However, ITO film must be deposited from a vapour in a process that is reportedly slow and, once the ITO is in the device, it cracks easily. Indium is also an expensive rare-earth element, costing as much as $800 (£512) per kilogram.

These problems have driven worldwide efforts to find less expensive materials that can be coated or printed like ink at much faster speeds to make low-cost, transparent conducting films, Wiley said.

One alternative to an ITO film is to use inks containing silver nanowires. The first mobile phone with a screen made from silver nanowires will be on the market this year, but silver, like indium, is still relatively expensive at $1,400/kg.

Copper is 1,000 times more abundant than indium or silver and about 100 times less expensive, costing only $9/kg.

In 2010, Wiley and his graduate student Aaron Rathmell showed that it was possible to form a layer of copper nanowires on glass to make a transparent conducting film. Simultaneously, the performance of the film was not good enough for practical applications because the wires clumped together. The new way of growing the copper nanowires and coating them on glass surfaces eliminates the clumping problem, Wiley said.

He also created the copper nanowires to maintain their conductivity and form when bent back and forth 1,000 times. In contrast, ITO films’ conduction and structure break after a few bends.

Wiley said that the low cost, high performance and flexibility of copper nanowires make them a natural choice for use in the next generation of displays and solar cells. He co-founded a company called NanoForge in 2010 to manufacture copper nanowires for commercial applications.

With continuing development, copper nanowires could be in screens and solar cells in the next few years, which could lead to lighter and more reliable displays, as well as making solar energy more competitive with fossil fuels, Wiley said.

Results from the research were published online in Advanced Materials on 23 September.