The temperature- and frequency-dependent ac conductivity of nanoporous metal-oxide semiconductors commonly
used in technologies for solar photoconversion is analyzed by using a model based on fluctuation-induced tunneling
conduction (FITC). The model takes into account voltage fluctuations of potential barriers that limit electron
transport at nanoparticle contact junctions. In contrast to previous models, quantitative agreement over the
entire temperature range studied is found by using the FITC model based on a single set of parameters. Guidelines
for the design of new materials for dye-sensitized solar cells (DSSCs) and solar photocatalysis are discussed.
The influence of surface hydration on the time-scales and mechanisms of interfacial electron transfer from rhodamine B
into SnO<sub>2</sub> is investigated. We combine molecular dynamics simulations and quantum dynamics propagation of transient
electronic excitations to analyze the regulatory role of water molecules affecting the adsorbate-semiconductor
interactions and the underlying electronic couplings that determine the electron injection times. The reported results are
essential to advance our understanding of interfacial electron transfer dynamics in dye sensitized semiconductor surfaces
at the molecule level, including fundamental interactions that affect the efficiency of interfacial electronic processes in
dye-sensitized solar cells as well as in a wide range of other technological applications.
Siloxanes with the general formula R-(CH<sub>2</sub>)<sub>n</sub>-Si-(OR')<sub>3</sub> form durable bonds with inorganic materials upon hydrolysis of
labile -OR' groups, and serve as robust coupling agents between organic and inorganic materials. In the field of dye-sensitized
solar cells, functionalization of TiO<sub>2</sub> thin-films with siloxane adsorbates has been shown to be useful as a
surface-passivation technique that hinders recombination processes and improves the overall efficiency of light-to-electricity
conversion. However, the attachment of siloxane adsorbates on TiO<sub>2</sub> surfaces still remains poorly understood
at the molecular level. In this paper, we report the characterization of 3-(triethoxysilyl) propionitrile (TPS) adsorbates,
covalently attached onto TiO<sub>2</sub> surfaces. We combine synthetic methods based on chemical vapor deposition, Fourier
transform (FT) infrared (IR) spectroscopy and electronic structure calculations based on density functional theory (DFT).
We predict that trifunctional siloxanes form only 2 covalent bonds, in a 'bridge' mode with adjacent Ti<sup>4+</sup> ions on the
TiO<sub>2</sub> surface, leaving 'dangling' alkoxy groups on the surface adsorbates. Our findings are supported by the observation
of a prominent fingerprint band at 1000-1100 cm<sup>-1</sup>, assigned to Si-O-C stretching modes, and by calculations of binding
enthalpies at the DFT B3LYP/(LACVP/6-31G**) level of theory indicating that the 'bridge' binding (ΔH<sub>b</sub>= -55 kcal
mol<sup>-1</sup>) is more stable than 'tripod' motifs (ΔH<sub>b</sub>= -45 kcal mol<sup>-1</sup>) where siloxanes form 3 covalent bonds with the TiO<sub>2</sub>
surface. The alkoxysiloxane groups are robust under heat and water treatment and are expected to be particularly
relevant for analytical methods since they could be exploited for immobilizing other functionalities onto the TiO<sub>2</sub> surfaces.
Force field parameters for large scale computational modeling of sensitized TiO<sub>2</sub>-anatase surfaces are developed from ab initio molecular dynamics simulations and geometry optimization based on Density Functional Theory (DFT). The resulting force field, composed of Coulomb, van der Waals and harmonic interactions, reproduces the ab initio structures and the phonon spectra density profiles of TiO<sub>2</sub>-anatase nanostructures functionalized with catechol, a prototype of an aromatic linker commonly used to sensitize TiO<sub>2</sub> nanoparticles with Ru(II)-polypyridyl dyes. In addition, simulations of interfacial electron injection and electron-hole relaxation dynamics demonstrate the capabilities of the resulting molecular mechanics force-field, as applied in conjunction with mixed quantum-classical methods, for modeling quantum processes that are critical for the overall efficiency of sensitized-TiO<sub>2</sub> solar cells.