Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

TiO2 photocatalysis and related surface phenomena

Photoinduced reactivity of titanium dioxide

▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...

Synthesis and Characterization of Monodisperse Nanocrystals and Close-Packed Nanocrystal Assemblies

The photocurrent response of dye-sensitized, porous nanocrystalline TiO2 cells was studied as a function of light intensity, in both the time domain (photocurrent transient measurements) and the frequency domain (intensity-modulated photocurrent spectroscopy). The photocurrent transients are characterized by a fast and a slow component. The rise time of the transients was in the range of milliseconds to seconds and exhibited a power law dependence on light intensity with an exponent of −0.6 to −0.8. The response to a modulated light intensity is characterized by a depressed semicircle in the complex plane. The time constant obtained from these spectra exhibits the same power law dependence on light intensity. The transient response of these cells is dominated by electron transport in the TiO2 film, and the results are shown to be consistent with a diffusion model where the diffusion coefficient for electrons in the particle network is a function of the light intensity.

Electron transport in porous nanocrystalline tio2 photoelectrochemical cells

A quasi-solid-state photoelectrochemical cell employing a dye-sensitized, nanocrystalline TiO{sub 2} electrode and a polymer gel electrolyte has been fabricated. The cells show open-circuit voltages close to 0.6 V and short-circuit currents larger than 3 mA cm{sup -2} under 30 mW cm{sup -2} white light illumination. Fill factors and open circuit voltages of the cell are comparable to those of similar cells with liquid electrolytes. Overall energy conversion efficiencies of 3-5% have been achieved. Photocurrent transients have relatively long rise time constants, indicating that electron transport in the TiO{sub 2} electrodes is controlled by a trapping process. At high light intensity the photocurrent rise is followed by a decay process due to the limitation of ion transport in the electrolyte. 7 refs., 4 figs.

A Solid State, Dye Sensitized Photoelectrochemical Cell

The optical and electrochemical properties of nanocrystalline TiO{sub 2} electrodes in acidic aqueous solution are reported. Cyclic voltammetry, UV/vis/NIR attenuance, EPR, photocurrent spectroscopy, and electrochemical impedance measurements are presented. At negative applied potentials the TiO{sub 2} films turn black, and an EPR spectrum appears which we attribute to Ti(III) species. The results are described in terms of a model in which the reduction of TiO{sub 2} leads to band edge unpinning. 36 refs., 9 figs.

Fei Cao

Papers

Electron transport in porous nanocrystalline tio2 photoelectrochemical cells

A Solid State, Dye Sensitized Photoelectrochemical Cell

Electrical and optical properties of porous nanocrystalline TiO2 films

Solid State, Dye Sensitized Photoelectrochemical Cell.