Binding of bi-isonicotinic acid to anatase TiO2 (1 0 1)

The interaction between dye and semiconductor is a central aspect of dye-sensitized solar cells. We have in this paper studied the binding of the common ligand bi-isonicotinic acid (4,4′-dicarboxy-2,2′-bipyridine) to TiO2 anatase (1 0 1) surfaces by means of quantum chemical calculations. Different adsorption models were studied with carboxyl oxygens binding to surface Ti atoms, and the acidic protons bonded to surface oxygens. A moderately deformed surface-binding ligand with two 2 M-bidentate (bridge) dye-surface bonds is found to be more favourable than both the currently prevailing dye-sensitization model of an undeformed 1 M-monodentate (ester) binding adsorbate structure, and a 1 M-bidentate surface-binding adsorbate structure.