Metal oxide Graphene oxide nanocomposite thin film for optoelectronic applications

Abstract

This thesis deals with the study of the solution-processed wide band gap metal oxide (TiO2) - graphene oxide (GO) nanocomposite materials in thin film form for their optoelectronic applications, such as UV-photodetector and dye-sensitized solar cells (DSSCs). Here, we demonstarte the fabrication of individual metal oxide (TiO2) - graphene oxide (GO) nanocomposites, as well as hybrid nanostructures (ZnO NW/TiO2), with GO incorporation using an easy, cost-effective and simple sol-gel spin coating technique. The formation of GO-composited highly transparent nanocomposite thin films, comprised of the rutile phase of TiO2 nanoparticles, as well as hybrid nanostructures (ZnO NW/TiO2), has been confirmed through microstructural, morphological, optical, and electrical characterizations. Modification of optical and electrical characteristics with a small amount of GO reinforcement into the host TiO2, as well as hybrid nanostructures (ZnO NW/TiO2), is also examined. Due to the incorporation of a small amount of GO into metal-oxide films, as well as hybrid nanostructures, the optical band gap values of those nanostructures are slightly reduced. At room temperature, DC bias dependent impedance spectroscopic analysis of TiO2 as well as hybrid nanocomposites (ZnO NW/TiO2) with GO, was performed for various external bias voltages in the frequency range of 4 Hz to 5 MHz. To evaluate and analyze the various contributions originating from the core grains and grain boundaries, the experimental Nyquist plot derived from the bias-dependent impedance spectra was fitted with an appropriate model electrical circuit consisting of two parallel RC circuits combined with a series resistance. The modification of grain boundary and its consequential effect on charge transport in individual metal oxide semiconductors, as well as hybrid nanocomposites, were confirmed by the variation of relaxation times (and#964; = RC) with an external bias and its modification after graphene oxide (GO) reinforcement. This demonstrates that a conducting graphene oxide