Theoretical Studies of Photoinduced Electron Transfer in Dye-Sensitized TiO2

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.