Water Contamination Effect on Liquid Acetonitrile/TiO₂ Anatase (101) Interface for Durable Dye-Sensitized Solar Cell

We have investigated the structural and electronic properties of liquid acetonitrile (MeCN)/TiO 2 anatase (101) interfaces involving a water molecule in order to analyze effect of ubiquitous water contamination in the typical electrolyte solution on the durability of dye-sensitized solar cell (DSSC), by using density-functional molecular dynamics simulations at room temperature. Our results show that H 2 O does not dive into the unbound Ti 5C sites on the (101) surface kinetically, once the coverage of MeCN is saturated (Θ ≈ 0.6). However, H 2 O adsorption through hydrogen bond with surface O 2C sites, not a Ti 5C site, is found the most stable if MeCN solvent is introduced to H 2 O-preadsorbed TiO 2 anatase (101) surface. This no-adsorption character of Ti 5c site in the aprotic solvent MeCN is in stark contrast to the case where the (101) surface is immersed by H 2 O layer or liquid H 2 O. The adsorbed H 2 O molecule via the hydrogen bond between O 2C and H W has its 1b 1 orbital at an energy just below the valence band maximum of TiO 2 . Therefore, this H 2 O has a sufficient possibility to become a cation radical by capturing hole generated by irradiation, which may attack the dye molecules toward the desorption. We thus demonstrate that removing H 2 O from the anatase (101) surface prior to introduction of the MeCN electrolyte solution is crucial to make the DSSCs more durable and efficient.