Modeling the Electronic Properties and Absorption Spectrum of Dye-Sensitized TiO2

Lin1, G. Fratesi2,1, S. Selçuk3, G.P. Brivio1 and A. Selloni3

1.Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, I-20125, Milano, Italy

2.Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133, Milano, Italy

3.Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States

We investigated the adsorption of prototypical dyes (catechol and isonicotinic acid) on the TiO2 anatase (101) and rutile (110) surfaces by means of Ab initio molecular dynamics simulations and time-dependent density functional calculations. We found that thermal fluctuation induce changes in the alignment of the molecular levels with the TiO2 valence band edge. These changes have a significant effect on the absorption spectrum of the anatase (101) surface, whose sensitization can be improved by increasing the hybridization between the adsorbed dye and TiO2 states. Sensitization effects are instead less relevant for the rutile (110) surface. As an extension towards more realistic materials for applications, we further studied two more complex molecular species, namely PTCDI and PTCDA, adsorbed on the TiO2 rutile (110) surface. These molecules have a more pronounced sensitization effect with a substantial red-shift of the first peak of the dye/TiO2 absorption relative to the free dye.

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