June 18, 2009 — Carbon Nanotubes (CNTs) and graphene exhibit extraordinary electrical properties for organic materials, and have a huge potential in electrical and electronic applications such as sensors, semiconductor devices, displays, conductors and energy conversion devices (e.g., fuel cells, harvesters and batteries). A new report from IDTechEx brings all of this together, covering the latest work from 78 organizations around the World to details of the latest progress applying the technologies.
Depending on their chemical structure, carbon nanotubes (CNTs) can be used as an alternative to organic or inorganic semiconductors as well as conductors, but the cost is currently the greatest restraint. However, that has the ability to rapidly fall as new, cheaper mass production processes are established, states the report.
In electronics, other than electromagnetic shielding, one of the first large applications for CNTs will be conductors. In addition to their high conductance, they can be transparent, flexible and even stretchable. Here, applications are for displays, replacing ITO; touch screens, photovoltaics and display bus bars and beyond.
In addition, interest is high as CNTs have demonstrated mobilities which are magnitudes higher than silicon, meaning that fast switching transistors can be fabricated. In addition, CNTs can be solution processed, i.e. printed. In other words, CNTs will be able to provide high performing devices which can ultimately be made in low cost manufacturing processes such as printing, over large areas.
They have application to supercapacitors, which bridge the gap between batteries and capacitors, leveraging the energy density of batteries with the power density of capacitors and transistors. Challenges are material purity, device fabrication, and the need for other device materials such as suitable dielectrics. However, the opportunity is large, given the high performance, flexibility, transparency and printability. Companies that IDTechEx surveyed report growth rates as high as 300% over the next five years.
While manufacturers in North America focus more on single wall CNTs (SWCNTs); Asia and Europe, with Japan on top and China second, are leading the production of multi wall CNTS (MWCNTs) with Showa Denko, Mitsui and Hodogaya Chemical being among the largest suppliers. The split of number of organizations working on the topic by territory is shown.
A number of companies are already selling CNTs with metallic and semiconducting properties grown by several techniques in a commercial scale but mostly as raw material and in limited quantities. However, the selective and uniform production of CNTs with specific diameter, length and electrical properties is yet to be achieved in commercial scale. A significant limitation for the use of CNTs in electronic applications is the coexistence of semiconducting and metallic CNTs after synthesis in the same batch. Several separation methods have been discovered over the last few years which are covered in the report, as is the need for purification.
Opportunities for Carbon Nanotube device manufacture
There are still some hurdles to overcome when using printing for the fabrication of thin carbon nanotube films. There is relatively poor quality of the nanotube starting material, which mostly shows a low crystallinity, low purity and high bundling. Subsequently, purifying the raw material without significantly degrading the quality is difficult. Furthermore there is also the issue to achieve good dispersions in solution and to remove the deployed surfactants from the deposited films, according to the report.