A quantum-mechanical study of the adsorption of prototype dye molecules on rutile-TiO2(110): a comparison between catechol and isonicotinic acid

In this work we present a theoretical investigation of the attachment of catechol and isonicotinic acid to the rutile-TiO2(110) surface. These molecules can be considered as prototypical dyes for use in Gra¨tzel type dye sensitised solar cells (DSCs) and are often employed as anchoring groups in both organic and organo-metallic sensitisers of TiO2. Our study focuses on determining the lowest energy adsorption mode and discussing the electronic properties of the resultant hybrid interface by means of density functional theory (DFT) calculations using the hybrid exchange (B3LYP) functional. We find that both molecules adsorb dissociatively at the TiO2 surface giving a type II (staggered) heterojunction. Compared to isonicotinic acid, catechol, due to the greater hybridisation of its molecular orbitals with the states of the substrate, is seen to enhance performance when employed as an anchoring group in dye sensitised solar cells.