Theoretical Studies of Photoinduced Electron Transfer in Dye-Sensitized TiO₂

Abstract

This review describes recent research into the properties of the chromophore-TiO2 interface that forms the basis for photoinduced charge separation in dye-sensitized semiconductor solar cells. It focuses particularly on an atomistic picture of the electron-injection dynamics. The interface offers an excellent case study, pertinent as well to a variety of other photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. The differences between chemists' and physicists' models for describing molecules and bulk materials, respectively, create challenges for the characterization of interfaces that include both of these components. We give an overall picture of the interface by starting with a description of the properties of the chromophores and semiconductor separately, and then by discussing the coupled system, including the chromophore-semiconductor binding, electronic structure, and electron-injection dynamics. Explicit time-dependent modeling is particularly valuable for an understanding of the ultrafast electron injection because it shows a variety of individual injection events with well-defined dynamical features that cannot be made apparent by an average reaction-rate description.

Visible-induced photocatalytic reactivity of polymer–sensitized titania nanotube films

“…The excited electrons on the CB of TiO 2 will accumulate and resist any electrons transfer from the photoexcited states of polythiophene. Consequently, the electrons on the CB of TiO 2 either delocalize inside TiO 2 bulk or eventually find its way to transfer into the ground state of polymer [14]. Moreover, the coating of polythiophene not only lowers down the extent of TNT crystallinity (see XRD spectrum in Fig.…”

“…1 are possible. Efficient electron injection into the edge of the CB avoids the energy loss by relaxation to the CB edge [14]. The injected electron delocalizes from bulk to surface, simultaneously relaxing to the bottom of the CB owing to coupling to vibrations.…”

A perspective on using experiment and theory to identify design principles in dye-sensitized solar cells

“…A 2007 review of modelling electron-injection dynamics concluded with seven summary points, one of which stated that ‘The average behaviour … is relatively independent of these specifics and can be predicted from a small number of concepts …’ [80]. With the increasing availability of more complex computational techniques, and the accumulated experience that modelling artefacts might have influenced results, it remains to be seen whether the same seven points are applicable in 2018.…”

Effects of Nuclear Vibrations on the Energetics of Polythiophene: Quantized Energy Molecular Dynamics

“…[1,5,[8][9][10] Nuclear motions also modulate electronic energy levels, which results in (i) a vibrational broadening of the adsorption spectrum [11] and (ii) changes in energy level matching between the donor and the acceptor. [9,10,[12][13][14][15] We have shown that nuclear dynamics can cause significant changes in the absorption properties and energy level matching between the donor and the acceptor in DSSC, likely causing changes in the electron injection rate by a factor of 2-3 as well as changes in the recombination rate by orders of magnitude. [12][13][14][15] With ab initio molecular dynamics (MD) simulations, it was possible to estimate the distribution over nuclear vibrations of frontier orbitals, the band gap, and driving forces to injection and regeneration.…”