Utilization of Single Walled Carbon Nanotubes in Electronic Applications and Solar Cell Devices

The discovery of single walled carbon nanotubes (SWNTs) has inspired expanding opportunities for use in a wide range of applications from electronics to medicine. Successful performance enhancement in applications, however, often requires uniform and stable dispersions of carbon nanotubes. Moreover, for further advancement of large scale electronic applications, facile methods to orient and align SWNTs are critical to the performance of these SWNT-enabled technologies. While microfluidic assembly of SWNTs has received significant interest, achieving desirable SWNT dispersion and morphology in fluids without an insulating surfactant or toxic superacid is challenging. Recent research has shown that SWNT alignment can reduce the resistivity as compared to a randomly oriented film. Thus, we will present a technique to overcome the critical challenge of aggregation in SWNTs, and to obtain highly conductive aligned films of SWNTs from water suspensions, uniquely producing a non-corrosive ink that can be directly applied to a device in-situ. The technique developed, urea functionalization on the SWNTs, utilizes binding between the amine group of urea and the carboxylic acid group of functionalized SWNTs and improves dispersion of the SWNTs in water. Compared with SWNTs dispersed using conventional methods (e.g. superacid and surfactants), the dispersed urea-SWNT aggregates have a higher aspect ratio with more rod-like morphology, implying less compact and more dispersed SWNTs. The Mayer Rod technique is used to prepare urea-SWNT highly aligned films (2D nematic order parameter of 0.6, 5 micron spotsize) with resistance values as low as 15-1700 ohms/sq in a transmittance range of 2-80% at 550 nm. These values compete with the best literature values to date for conductivity of SWNT-enabled thin films. The findings offer promising opportunities for industrial applications relying on highly conductive thin SWNT films.;Lastly, to make a major impact in photovoltaic devices, it is necessary to implement a transformative technology. The advances in utilizing quantum dots in solar cell devices offer new opportunities to make such a difference. Coupling quantum dots with SWNTs to make hybrid nanocomposites in organic/inorganic solar cells has been widely studied. SWNTs and CdSe QDs offer complementary characteristic and attractive properties for energy transport and charge collection. In this thesis, we will present a novel technique to directly attach CdSe QDs to SWNTs to increase the solar cell efficiency. The materials were investigated and optimized to enhance the carrier mobility and charge transfer and the properties of the bound CdSe and SWNT suggest the formation of a strong coupled nanocomposites, enabling access to new optoelectronic properties for the nanocomposite. The solar cells fabricated with SWNT-CdSe nanocomposite doubled the solar cell performance as compared to the cells fabricated with SWNTs alone.