  Electrodes in dye sensitised solar cells (DSSCs) are typically
nanocrystalline anatase TiO2 with a majority (101) surface exposed. Generally
the sensitising dye employs a carboxylic anchoring moiety through which it
adheres to the TiO2 surface. Recent interest in exploiting the properties of
differing TiO2 electrode morphologies, such as rutile nanorods exposing the
(110) surface and anatase electrodes with high percentages of the (001) surface
exposed, begs the question of whether this anchoring strategy is best,
irrespective of the majority surface exposed. Here we address this question by
presenting density functional theory calculations contrasting the binding
properties of two promising anchoring groups, phosphonic acid and boronic acid,
to that of carboxylic acid. Anchor-electrode interactions are studied for the
pro- totypical anatase (101) surface, along with the anatase (001) and rutile
(110) surfaces. Finally the effect of using these alternative anchoring groups
to bind a typical coumarin dye (NKX- 2311) to these TiO2 substrates is
examined. Significant differences in the binding properties are found depending
on both the anchor and surface, illustrating that the choice of anchor is
necessarily dependent upon the surface exposed in the electrode. In particular
the boronic acid is found to show the potential to be an excellent anchor
choice for electrodes exposing the anatase (001) surface.
