A Theoretical Study Of Electron Transfer In TiO₂ Nanotube Based DSSCs

Dye sensitized solar cells?DSSCs?have become the focus of attention and research for the majority of researchers due to their simple manufacturing process,low production cost,high stability and optical-electric conversion efficiency.DSSCs are mainly made up by semiconductor thin film,photosensitive material?dye molecule?,electrolyte,counter electrode and conductive substrate.In a titanium dioxide based DSSC,the semiconducting material?s nanocrystalline morphology is one of the important factors that may influence the optical-electric conversion efficiency.In recent years,in the study of DSSCs,researchers tried to replace the traditional TiO₂ materials with TiO₂ nanotube?TiO₂ NT?layers.This is because the TiO₂ nanotube layers show a high degree of order in structure,which can provide one-dimensional electron transfer pathway,and they are expected to significantly improve the charge transfer efficiency of the solar cells.However,there are still lack of detailed theoretical models of electron transfer mechanisms between dye and TiO₂NT and within TiO₂ NT.Therefore,in this study,one-dimensional TiO₂ NT was taken as the subject to research,and the composed systems of dye molecule adsorbed on TiO₂ NT were calculated in detail,so as to further explore the electron transport mechanisms at the dye/TiO₂ NT interface and on the nanotubes.In this study,a series of theoretical studies have been carried out on the composed systems of two different kinds of dye molecules?bearing the carboxylate and the hydroxamate anchors,respectively?and TiO₂ NTs.Our results show that the structure of?12,0?TiO₂ NT is similar to that of anatase,while the?0,4?TiO₂ NT shows obvious structural deformation along the direction that is vertical to the axis of nanotube.Compared with carboxylate anchor,the highly water-stable hydroxamate anchor exhibits better light-harvesting ability.In addition,the hydroxamate anchor group also exhibits a slightly stronger binding to the TiO₂ NT surface than the carboxylate anchor group.The interfacial electron transfer?IET?dynamics reveal that compared with bulk TiO₂,both of the two TiO₂ NTs can accelerate the electron transfer between the dye and TiO₂ layers.Moreover,the plots of electronic isosurfaces?time evolution of the electron clouds?indicate the electron transfer mechanisms of?12,0?and?0,4?TiO₂ NTs are different.In?12,0?TiO₂ NT,the optical-excited electrons can transfer on the surface of the nanotube with directions both parallel and vertical to the nanotube axis.While for?0,4?TiO₂ NT,the electrons can only transfer on the surface along the nanotube axis.We hope that our research can reveals the working mechanism of one-dimensional TiO₂ NT in dye sensitized solar cells and provides help for design better DSSCs systems.