Quantum Photoelectrochemistry

Interactions between organic molecules and transition metal oxide surfaces have been investigated by means of quantum chemical calculations. The studies have been aimed at understanding electrode-adsorbate interactions in photoelectrochemical devices, such as dye-sensitized solar cells.

Structural properties of the interface between metal oxide surfaces and organic adsorbates have been investigated for formic acid on a ZnO surface, and for bi-isonicotinic acid on TiO2 surfaces. Questions of surface-adsorbate binding, adsorbate- adsorbate interactions, surface relaxations, and sensitizer strain have been considered. Relevant to the solar cells is the finding that strong sensitizer-anchoring via carboxyl groups is compatible with moderate sensitizer deformations.

Electronic effects have been studied for aromatic molecules adsorbed on TiO2surfaces and nanocrystals. Electronic coupling strengths, substrate-induced changes to the adsorbate electronic structure, and mechanisms of electron injection are discussed.

The calculations have been made with semiempirical, periodic Hartree-Fock, anddensity functional methods. Semiempirical parameters are presented for systemscontaining both organic molecules and transition metal oxide surfaces. Much ofthe theoretical work has been successfully combined with data from XPS and XASexperiments

More generally, this thesis demonstrates the capability of quantum chemical calculations to address important questions regarding molecular properties of sensitized metal oxide electrodes, and the prospects of such quantum photoelectrochemistry is discussed.