Infrared Nanotube Films Offer Advantages for Solar Cells and More

Researchers have found that nanotube films have very good infrared transmission that could improve the efficiency of infrared solar cells. Image credit: Royal Society of Chemistry.

(PhysOrg.com) -- Researchers have already known that carbon nanotube thin films have mechanical and conductive advantages that could make them useful as electrodes in solar cells, solid state lighting, and electronic displays. However, studies so far have focused on how well nanotube films transmit light in the visible range, but have not explored the films’ infrared properties.

In a recent study, physicists Liangbing Hu, David Hecht, and George Grüner from the University of California, Los Angeles, have investigated the infrared properties of single-walled carbon nanotube thin films that are optically transparent and electrically conductive. They found that the nanotube films have an outstanding ability for transmitting infrared waves. In experiments, nanotube electrodes and graphene electrodes outperformed various other materials in several key categories, opening up a variety of infrared applications for the nanotube films.

“This is the first time that the infrared properties of conductive CNT films are fully studied through measurement and calculations,” Hu told PhysOrg.com.

To fabricate the nanotube films, the scientists dispersed nanotubes in water with the help of a surfactant, and then sprayed the substance onto heated substrates to create films. When shining an infrared light on the nanotube films, the scientists found that the films maintained an average transmittance rate of more than 90% over a wide infrared wavelength range (450 nanometers - 20 micrometers).

Because of the nanotube films’ high infrared transmittance, the scientists explain that they would make poor candidates for blocking heat, but would be useful for applications that require heat dissipation. One prominent example is solar cells. Since a large portion of solar energy is above a wavelength of 1 micrometer (longer than optical wavelengths), transparent nanotube thin films could be used to capture excess heat in infrared solar cells, making the solar cells more efficient.

“One major application is the infrared solar cells, where transparent CNT films as well graphene films would allow the transmission of infrared energy to the active layer, which allows the fabrication of infrared solar cells,” Hu said.

Compared with other materials known to transmit infrared waves, the nanotube films have the lowest reflection rate (less than 10%) of those addressed in the study. This advantage means that nanotube films might not require an antireflective coating like the others. In addition, nanotube films have high cutoff wavelengths (they transmit longer infrared wavelengths) compared with the other materials. This property could make the films especially useful for applications in the far infrared range.

The films could also serve as electrodes for a variety of industrial and military applications, such as infrared imaging, sensing, and emission, as well as modulators for fiber communications. Hu added that, in the future, the researchers plan to investigate using the films for an infrared camera.

More information: Hu, Liangbing; Hecht, David S.; Grüner, George. “Infrared transparent carbon nanotube thin films.” Applied Physics Letters 94, 081103 (2009).

Cambridge, Nokia introduce new stretchable and flexible mobile phone concept

Morph Wrist Mode

The concept for a new stretchable and flexible mobile phone developed by the University of Cambridge and the Nokia Research Center (NRC) was unveiled today.

Morph, the joint nanotechnology concept, launches today alongside the new Design and the Elastic Mind exhibition at The Museum of Modern Art (MoMA) in New York City in which it is profiled. The exhibition will be on view from 24 February to 12 May 2008.

Morph Phone Mode

Morph is a concept that demonstrates how future mobile devices might be stretchable and flexible, allowing the user to transform their mobile device into radically different shapes. It demonstrates the ultimate functionality that nanotechnology might be capable of delivering: flexible materials, transparent electronics and self-cleaning surfaces.

Professor Mark Welland, Head of the Department of Engineering's Nanoscience Group at the University of Cambridge and University Director of Nokia-Cambridge collaboration, commented: "Developing the Morph concept with Nokia has provided us with a focus that is both artistically inspirational but, more importantly, sets the technology agenda for our joint nanoscience research that will stimulate our future work together."

Dr. Tapani Ryhanen, Head of the NRC Cambridge UK laboratory, Nokia, added: "We hope that this combination of art and science will showcase the potential of nanoscience to a wider audience. The techniques we are developing might one day mean new possibilities in terms of the design and function of mobile devices. The research we are carrying out is fundamental to this as we seek a safe and controlled way to develop and use new materials."

The partnership between the University of Cambridge and Nokia was announced in March, 2007 - an agreement to work together on an extensive and long term programme of joint research projects.

NRC has established a research facility at the University's West Cambridge site and collaborates with several departments initially the Department's Nanoscience Center and the Electrical Division of the Engineering Department on projects that, to begin with, are centered on nanotechnology.

A video on this new technology is available to watch the Nokia website: http://www.nokia.com/A4879144