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Cu nanowires to replace ITO films

Posted: 10 Oct 2011     Print Version  Bookmark and Share

Keywords:copper nanowire  conductive films  ITO 

A recent study shows that the copper nanowire films have the same properties as those currently used in electronic devices and solar cells. The films that currently connect pixels in mobile displays are made of indium tin oxide (ITO). The copper atoms can be organised in water to create long, thin and non-clumped nanostructures that can be made into transparent conductive films.

Duke University chemist, Ben Wiley, and his graduate student, Aaron Rathmell, have devised a method to make nanowires film from copper that can be coated into glass or plastic. It is said to be highly transparent, enabling it to transmit information well at lesser manufacturing cost. However, the ITO film must be deposited from a vapour in a process that is a 1000x slower than newspaper printing and. Once the ITO is in the device, it also cracks easily. Indium is an expensive rare earth element, costing as much as Rs.0.36 lakh/kg ($800/kg).

copper nanowire

A new flexible film made of copper nanowires and plastic conducts electricity illuminating a small light bulb. Credit: Ben Wiley, Duke University.

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 stated. One alternative to an ITO film is to use inks containing silver nanowires. The first cell phone with a screen made from silver nanowires will be on the market this year. However, silver is also expensive at Rs.0.63 lakh/kg ($1400/kg). Copper, on the other hand, is 1000x more abundant than indium or silver, and about 100x less expensive at only Rs.403.59 ($9/kg), the researchers said.

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

They also created the copper nanowires to maintain their conductivity and form when bent back and forth 1,000x. In contrast, ITO films' conduction and structure break after a few bends. Wiley said the low-cost, high-performance and flexibility of copper nanowires make them a natural choice for the next generation of mobile displays and solar cells.

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

- Julien Happich
  EE Times

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