Theoretical studies on spectroscopic properties of ruthenium sensitizers absorbed to TiO2 film surface with connection mode for DSSC

Electron injection from a photoexcited chromophore into the surface of mesoscopic semiconductor TiO2 nanoparticles is one of the key electron transfer processes for DSSC. A reasonable and reliable TiO2 surface model (dropped down the anatase (101) and rutile (110) crystals a slab model) was designed, which was employed to investigate the absorption behavior of the adsorbed dye molecules such as C101, J13 and N749 under DFT method. According to the calculation results, the detailed orbital components and absorption transition are obtained; furthermore, the ultrafast, excited-state electron injection and emission electron injection can be discriminated. Generally, both the connecting surfaces of TiO2 and degree of deprotonating dye molecules could influence absorption spectrum intensely. Our calculations show that the more efficient DSSCs should have larger conjugation degree for ancillary ligands or the whole system, which is beneficial to photon absorption from the visible to near-IR region.

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► A reasonable and reliable TiO2 surface model was designed.
► Ultrafast excited- and emissive electron injection were discriminated.
► The connecting surface type of TiO2 film affects the absorption spectrum.
► The degree of deprotonation of dye influences excitation energy of whole system.