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Self-assembled nanotubes exhibit photoconductivity

02 Jan 2007

Japanese scientists have made highly photoconductive nanotubes that they believe could be used for photovoltaic applications.

"The nanotube, upon exposure to light, shows a large photoconductive response with an on/off ratio greater than 10,000," Takanori Fukushima told nanotechweb.org. "Such outstanding properties have never been realized at the nanometer-level by other conductive polymers and carbon-based materials."

The coaxial nanotubes, which are 16 nm in diameter, are formed by self-assembly from trinitrofluorenone-appended hexabenzocoronene molecules. The nanotubes consist of a layer of electron-accepting trinitrofluorenone (TNF) on an electron-donating graphitic layer of π-stacked hexabenzocoronene.

The separation between the two types of molecules is crucial to the photoconductivity – if the donor and acceptor molecules are close together they form charge-transfer assemblies where photochemically generated charge carriers become trapped and recombine.

"We believe that the coaxial nanotube we obtained will provide an ultimate molecular design strategy to achieve an extraordinary wide interface for the donor-acceptor heterojunction," said Fukushima.

"Considering the extremely long-range one-dimensionality, along with the large on/off ratio of the photoconductive response, our coaxial nanotube could have a great potential in optoelectronic applications such as nanoscale photovoltaics and photo-detectors," he added.

Now the team hopes to realize highly efficient nanoscale photovoltaics by aligning the photoconductive nanotubes unidirectionally and by improving their contact with the electrodes. "Incorporation of electron-accepting functionalities other than TNF into the coaxial nanotubular architecture should also deserve further studies," said Fukushima.

The researchers reported their work in Science.

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