Carbon nanotube diode aimed for solar cells

This is an improvement upon the original nanotube diode device that GE Global Research (Niskayuna, N.Y.) developed and announced last year.

"GE's success in developing the 'perfect' carbon nanotube device has not only ushered in a new era in electronics, it has potentially opened new doors in solar energy research," said Margaret Blohm, GE's advanced technology leader for nanotechnology, in a statement. "The discovery of a photovoltaic effect in our nanotube device could lead to exciting breakthroughs in solar cells that make them more efficient and a more viable alternative in the mainstream energy market.”

Unlike traditional diodes, GE's carbon nanotube device has the ability to perform multiple functions — as a diode and two different types of transistors — which should enable it to both emit and detect light. .

Diodes are formed by joining a p-type and an n-type semiconducting material. In the GE device, the two regions were formed using an electrostatic doping technique using two separate gates that couple to two halves of a single carbon nanotube. By biasing one gate with a negative voltage and the other with a positive voltage, a p-n junction can be formed.

GE scientists discovered that an ideal diode could be realized by suspending the middle portion of the carbon nanotube where the carrier recombination occurs. These results show that carbon nanotubes can be very sensitive to the substrate that they are in contact and provide important clues to the fundamental workings of any carbon nanotube based devices.

The scientists further elaborated on the ideal diode behavior by examining their photovoltaic properties, the process in which light energy is converted to electricity. Despite being some 1000 times smaller than the wavelength of light, the carbon nanotube diodes showed significant power conversion efficiencies owing to the enhanced properties of an ideal diode.

The development is part of a major program at GE. Under the so-called Ecomagination program, GE has pledged to more than double its level of investment in the development of new technologies from $700 million to $1.5 billion over the next five years. As part of this commitment, GE Global Research has an active program in photovoltaics that is investigating how to generate power from sunlight more cost effectively and more efficiently.