New Approaches to Organic-Inorganic Interfaces for Solar Energy Applications

This thesis is composed of three parts. First, is the discovery of a new method for functionalizing TiO2 for dye-sensitized solar cell applications is discussed. This discovery is the primary focus of this thesis. Second, there is a focus on the surface chemistry and development of surface pretreatments for GaN and graphene prior to atomic layer deposition of high-kappa dielectrics. Finally, studying the optoelectronic properties of earth-abundant, non-toxic materials of interest for harvesting solar energy, and developing a new experimental technique for spatial resolution of surface photovoltage concludes this thesis.;The bulk of research performed has primarily been about discovering thermal grafting of small aromatic molecules to TiO2 surfaces. Small benzyl and aryl molecules have successfully been attached to TiO2 using no additional linker groups and mild, additive-free reaction conditions. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FTIR) characterized the molecular surface coverage.;Further examination has been performed of how the molecular electron density influences the reaction rate and thermodynamic stability of the molecule-metal oxide interface formed through thermal grafting. Reaction rates were determined for the TiO2 thin film functionalization using molecules exhibiting a wide range of electron density and monitoring the reactions using FTIR. Enthalpies of adsorption for a wider range of molecules on the anatase TiO 2(001) surface were computed to determine how substituent electrostatics affect the thermodynamic stability of the molecule-surface bond. Experimental and computational Hammett Plots were made in order to establish connections between substituent effects and reaction mechanism. These plots indicated that thermal grafting is not noticeably affected by substituent effects.;The effects of the surface water layer were studied for potential influence on the rate limiting step. Variable temperature NMR was used to determine the water solubility of each aryl halide used in functionalization, and in-situ mass spectrometry and attenuated total reflectance FTIR were performed to monitor loss of water as the reaction occurs. These experiments indicate the water layer has no apparent influence on the rate of reaction, leading to the conclusion that there is something much more complex behind the thermal grafting of iodo aryl species to TiO2 surfaces.