Process to make high performance carbon nanotube 'Inks' with electrical characteristics well-suited for plastic electronics

27-Jan-09

Scientists at DuPont and Cornell University have used a simple chemical process to convert "as grown" mixtures of metallic and semiconducting carbon nanotubes into solely semiconducting carbon nanotubes with electrical characteristics well-suited for plastic electronics. This new finding identifies a commercially viable path for the production of bulk quantities of organic semiconducting ink, which can be printed into thin, flexible electronics such as transistors and photovoltaic materials for solar cell technology. Since their discovery in the early 1990s, there has been great interest in the revolutionary electrical, mechanical and thermal properties of carbon nanotubes. However, the fact that carbon nanotubes are produced as complex mixtures can greatly limit their applications. The current development is a significant advancement in this pioneering field, and is a more promising approach to developing semiconductor applications of carbon nanotubes. A significant limitation in electronic application of carbon nanotubes has been the difficulty in separating metallic from semiconducting carbon nanotubes. The research uncovered a potentially low cost route to suppress the conductivity of the metallic tubes without requiring further separation of nanotubes by type. The group has developed a simple chemical process that brought fluorine-based molecules into contact with the nanotubes. Through a process called cycloaddition, the fluorine molecules efficiently attacked or converted the metallic nanotubes, leaving the semiconducting tubes alone, and creating a perfect batch of solely semiconducting nanotubes. The resulting carbon nanotubes were dispersed into semiconducting ink and used in thin film transistors that are designed to be thinner, lighter and use less energy. It appears that cycloaddition, as opposed to the standard monovalent attachment of molecules, provides an effective method for suppressing the conductivity of the metallic nanotubes in a very controlled fashion. The work suggests that careful control of the chemical reaction enables the suppression of metallic tubes without degradation of semiconducting tubes."