Influence of Seeding and Bath Conditions in Hydrothermal Growth of Very Thin (∼20 nm) Single-Crystalline Rutile TiO₂ Nanorod Films

New seeding conditions have been examined for the hydrothermal growth of single-crystalline rutile TiO₂ nanorods. Rutile nanorods of ∼20 nm diameter are grown from seed layers consisting of either (A) TiO₂ or MnOOH nanocrystals deposited from suspension, or (B) a continuous sheet of TiO₂. These seed layers are more effective for seeding the growth of rutile nanorods compared to the use of bare F-SnO₂ substrates. The TiO₂ sheet seeding allows lower concentration of titanium alkoxide precursor relative to previously reported procedures, but fusion of the resulting TiO₂ nanorods into bundles occurs at higher precursor concentration and/or longer growth duration. Performance of polymer-oxide solar cells prepared using these nanorods shows a dependence on the extent of bundling as well as rod height

Solid-State Photogalvanic Dye-Sensitized Solar Cells

Photogalvanic cells are photoelectrochemical systems wherein the semiconductor electrode is not a participant in primary photoinduced charge formation. The discovery of photoelectrochemical systems that successfully exploit secondary (thermal) electron injection at dye–semiconductor interfaces may enable studies of electron transfer at minimal driving force for electron injection into the semiconductor. In this study, we have examined thermal electron transfer from molecular sensitizers to nanostructured semiconductor electrodes composed of titanium dioxide nanorods by means of transient spectroscopy and the assembly and testing of photoelectrochemical cells. Electron-accepting molecular dyes have been studied alongside an arylamine electron donor. Thermal injection is estimated for a naphthacenequinone radical anion as a multiexponential decay process with initial decay lifetimes of 6 and 27 ps. The ambient electric field present during charge separation at a surface-adsorbed dye monolayer causes Stark shifts of the radical ion pair absorbance peaks that confounded kinetic estimation of thermal injection for a fullerene sensitizer. Electron-accepting dyes that operate by thermal injection into titanium dioxide function better in solid-state photoelectrochemical cells than in liquid-junction cells due to the kinetic advantage of solid-state cells with respect to photoinduced acceptor-quenching to form the necessary radical anion sensitizers

Electron Transport in Acceptor-Sensitized Polymer–Oxide Solar Cells: The Importance of Surface Dipoles and Electron Cascade Effects

Fullerene and acenequinone compounds have been examined as electron mediators between a p-type semiconductive polymer and two n-type oxide semiconductors. Composite interlayer materials and photovoltaic test cells were assembled and studied for their fluorescence quenching, current–voltage, and quantum efficiency behavior to characterize the efficacy of the acceptor-sensitizers as electron-selective interlayers. The sensitizers are generally more effective with titanium dioxide than with zinc oxide, due to the difference in magnitude of dipole-induced vacuum level shifts at the respective oxide interfaces. In titanium dioxide-based solar cells, where dipole effects are weak, photovoltage and fill factor increase in a trend that matches the increase in the first reduction potential of the acceptor-sensitizers. Photosensitization of the oxide semiconductor by the acceptor-sensitizers is observed to operate either in parallel with the polymer as an alternate photosensitizer or in series with the polymer in a two-photon process, according to an acceptor-sensitizer’s first reduction potential. In zinc oxide-based solar cells, where dipole effects are stronger, the acceptor-sensitizers impaired most devices, which is attributed to an upward shift of the oxide’s conduction band edge caused by dipole-induced vacuum level shifts. These results have broad implications for designing electron-selective interlayers and solid-state photocells using sensitized oxide semiconductors

UV-Assisted Modification and Removal Mechanism of a Fluorocarbon Polymer Film on Low‑<i>k</i> Dielectric Trench Structure

In this study, we report the first chemical characterization of a plasma-deposited model fluoropolymer on low-<i>k</i> dielectric nanostructure and its decomposition in UV/O₂ conditions. Carbonyl incorporation and progressive removal of fluorocarbon fragments from the polymer were observed with increasing UV (≥230 nm) irradiation under atmospheric conditions. A significant material loss was achieved after 300 s of UV treatment and a subsequent wet clean completely removed the initially insoluble fluoropolymer from the patterned nanostructures. A synergistic mechanism of UV light absorption by carbonyl chromophore and oxygen incorporation is proposed to account for the observed photodegradation of the fluoropolymer

Optoelectronic Tuning of Organoborylazadipyrromethenes via Effective Electronegativity at the Metalloid Center

Organoborylazadipyrromethenes were synthesized from free base and fluoroborylazadipyrromethenes and characterized with regard to their structural and electronic properties. B–N bond lengths, along with photophysical and redox behavior, appear dependent on the effective electronegativity at the boron atom as tuned by its substituents, with stronger electronegativity correlating to a shorter B–N bond length, red-shifted absorbance, enhanced fluorescence lifetime and yield, and positively shifted redox potentials

Templated Electrodeposition and Photocatalytic Activity of Cuprous Oxide Nanorod Arrays

Cuprous oxide (Cu₂O) nanorod arrays have been prepared via a novel templated electrodeposition process and were characterized for their photocatalytic behavior in nonaqueous photoelectrochemical cells. Zinc oxide (ZnO) nanorod films serve as sacrificial templates for the in situ formation of polymer nanopore membranes on transparent conductive oxide substrates. Nitrocellulose and poly­(lactic acid) are effective membrane-forming polymers that exhibit different modes of template formation, with nitrocellulose forming conformal coatings on the ZnO surface while poly­(lactic acid) acts as an amorphous pore-filling material. Robust template formation is sensitive to the seeding method used to prepare the precursor ZnO nanorod films. Photoelectrochemical cells prepared from electrodeposited Cu₂O films using methyl viologen as a redox shuttle in acetonitrile electrolyte exhibit significant charge recombination that can be partially suppressed by a combination of surface passivation methods. Surface-passivated nanostructured Cu₂O films show enhanced photocurrent relative to planar electrodeposited Cu₂O films of similar thickness. We have obtained the highest photocurrent ever reported for electrodeposited Cu₂O in a nonaqueous photoelectrochemical cell