Several aspects of dye-sensitized titanium dioxide colloidal thin films

Research on solar energy conversion devices based on dye-sensitized titanium dioxide semiconductor has been an active area of research during the past decade. Numerous efforts have been made to understand the fundamental sensitization mechanism and improve the solar cell efficiency. Several aspects of sensitizer-TiO ₂ interaction have been explored in this thesis. In Chapter 2, sensitizers with low-lying ligand field states have been synthesized and bound to TiO ₂ surfaces. An unprecedent temperature-dependent interfacial electron injection has been observed for sensitizer Ru(bpy)₂(ina)₂ 2+, where bpy is bipyridine and ina is isonicotinic acid. A model is proposed where the direct population of ligand field states competes kinetically with electron injection. In Chapter 3, we found that surface proton concentration has a profound impact on sensitizer surface attachment, intermolecular RuIII/II electron “hopping”, and the excited state electron injection quantum yield. Synthetic endeavors that have provided a new strategy for studying fixed distance electron transfer at nanoparticle interfaces are described in Chapter 4. The first proof-of-concept experiments with metal oxide nanocrystallites have resulted in rapid (k_et > 108 s−1) interfacial electron transfer over an 18 Å distance. Chapter 5 described a series of ruthenium complexes based on 2,2′-bipyridine ligands with phosphonic acid groups bound directly or through a methylene spacer to the 4,4′ or 5,5′ position of bipyridine. Interfacial electron injection quantum yield measurements provided insights into how small variations in the sensitizer-semiconductor architecture can influence the sensitization efficiency. Porphyrin sensitized TiO₂ were studied in Chapter 6. Orbital perturbations have been observed upon loading the porphyrins onto TiO₂ surfaces, presumably through the interaction between the carboxylic acid anchoring groups and the semiconductor surface. The performance of the porphyrins in dye-sensitized cells was influenced by porphyrin peripheral substitutents, central metal, and electronic active positions in the macrocycle.