Single Wall carbon NanoTubes (SWNTs) offer excellent electronic and mechanical properties making them suitable for a vast range of potential applications. Researchers at Florida International University, in a project funded by the the Air Force Office of Scientific Research at the U.S. Department of Defense, have shown that controlling the length of SWNTs can improve their photoelectrochemical activity, opening opportunities in the fabrication of efficient optoelectronic devices, nanotube optical detectors or emitters. (Chen-Zhong Li et al, doi:10.1016/j.electacta.2008.06.059)
The lab team implemented a fundamental study of the electron transfer phenomenon of bio and nano materials, such as DNA, carbon nanotubes, graphene, and their nano-bio complexes, including the study of the finite size effect on photo-induced electron transfer in carbon nanotubes. Although some previous studies have suggested that carbon nanotubes are photoelectrochemically active and generate photocurrent upon visible excitation, the team's results demonstrated that a more efficient conversion of photo-to-electric energy could be achieved by manipulating the nanostructure of the material.
Both cathodic and anodic photocurrents were observed on shortened SWNT formed thin films. The incident photon conversion efficiency was measured at eight-fold higher compared to the longer SWNTs, suggesting their electronic structure and photoelectrochemical properties were dramatically altered.
Team leader Chen-Zhong Li comments, “Although previous theoretical and experimental studies have predicted that carbon nanotubes have a tremendous potential application for photoelectronic application, the low photo-to-electricity conversion efficiency has limited the development for real applications.”
The higher efficiency seen in the conversion of photo-energy to electric energy will broaden the practical application of carbon nanotubes in solar energy and optoelectronic sensing devices. “This is a remarkable discovery, and the novel photo electrochemical activities of finite size carbon nanotube will allow us to improve the overall photo-to-electricity efficiency of solar energy conservation, the relative enhanced current induced by light irradiation will allow us to engineer highly sensitive optical sensors,” continues Dr Chen-Zhong Li.
The Florida team is now looking at the potential applications offered by the discovery. It is envisaged that the photo-to-electricity conversion efficiency can be further improved by using the assembly of finite-sized SWNTs with other semiconducting materials or photo sensitive polymers, the combined features of the complex materials making them ideal building blocks for future, new generation solar cell and photoelectronic devices.