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The development of future electronics depends on the availability of suitable functional materials. Printed electronics, for example, relies on access to highly conductive, inexpensive and printable materials, while strong light absorption and low carrier recombination rates are demanded in photocatalysis industry. Despite all efforts to develop new materials, it still remains a challenge to have all the desirable aspects in a single material. One possible route towards novel functional materials, with improved and unprecedented physical properties, is to form composites of different selected materials. In this work, we report on hydrothermal growth and characterization of graphene/zinc oxide (GR/ZnO) nanocomposites, suited for electronics and photocatalysis application. For conductive purposes, highly Al-doped ZnO nanorods grown on graphene nanoplates (GNPs) prevent the GNPs from agglomerating and promote conductive paths between the GNPs. The effect of the ZnO nanorod morphology and GR dispersity on the nanocomposite conductivity and GR/ZnO nanorod bonding strength were investigated by conductivity measurements and optical spectroscopy. The inspected samples show that growth in high pH solutions promotes a better graphene dispersity, higher doping and enhanced bonding between the GNPs and the ZnO nanorods. Growth in low pH solutions yield samples characterized by a higher conductivity and a reduced number of surface defects. In addition, different GR/ZnO nanocomposites, decorated with plasmonic silver iodide (AgI) nanoparticles, were synthesized and analyzed for solar-driven photocatalysis. The addition of Ag/AgI generates a strong surface plasmon resonance effect involving metallic Ag0, which redshifts the optical absorption maximum into the visible light region enhancing the photocatalytic performance under solar irradiation. A wide range of characterization techniques including, electron microscopy, photoelectron spectroscopy and x-ray diffraction confirm a successful formation of photocatalysts. Our findings show that the novel proposed GR-based nanocomposites can lead to further development of efficient photocatalyst materials with applications in removal of organic pollutants, or for fabrication of large volumes of inexpensive porous conjugated GR-semiconductor composites.

<p>Nanomaterials have been heavily studied in the past two decades. Previous findings have demonstrated that the characteristics of nanocomposites and the performance of nanomaterial-based devices are both determined by the interfacial characteristics of the nanomaterials. However, there are still some remaining challenges from interfacial characteristics to device applications, which are specified as follows: the difficulty in identifying the interfacial contacts of nanostructured surfaces, the instability of nanocomposite surfaces, and the under-researched mechanism of the correlation between interfacial characteristics and the performance of devices.</p> <p>Therefore, the main theme of this thesis is to investigate the interfacial contacts of nanostructured solid-liquid interfaces by direct observation, and to develop a stable nanocomposite based on which the direct observation of the interfacial contact can be better conducted, and to eventually investigate the effect of interfacial contacts on the performance of organic solar cells.</p> <p>As the previous identification of the solid-liquid interface is limited to a microscale range, a direct method of tracing the different wetting states of water was developed, on nanostructured surfaces. This method provided an answer to a long standing question of, whether there is a transition from Wenzel to Cassie states in the sliding angle drop on nanocomposite thin films. In order to complete the observation of the wetting states of water, a stable superhydrophobic nanocomposite thin film with hierarchical structure was developed.</p> <p>Furthermore, with the knowledge of identifying the wetting states and the preparing procedures of the nanocomposites, a surfactant-free small-molecule nanoparticle organic solar cell with a much improved fill factor was developed by spin coating. The inverse correlation of series resistance and parallel resistance was discovered, due to the morphology change and the variation of the charge carrier concentration near the donor-acceptor interface in small-molecule organic solar cells.</p> / Doctor of Philosophy (PhD)