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)/TiO2 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 H2O does not dive into the unbound Ti-5C sites on the (101) surface kinetically, once the coverage of MeCN is saturated (Theta approximate to 0.6). However, H2O 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 H2O-preadsorbed TiO2 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 H2O layer or liquid H2O. The adsorbed H2O 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 TiO2. Therefore, this H2O 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 H2O from the anatase (101) surface prior to introduction of the MeCN electrolyte solution is crucial to make the DSSCs more durable and efficient.