Aggregation of organic dyes on TiO2 in dye-sensitized solar cells models: an ab initio investigation.

A density functional theory (DFT), time-dependent DFT, and ab initio second order Møller-Plesset perturbation theory study of the aggregation of the metal free indoline D102 and D149 dyes on extended TiO(2) models is reported. By selecting the relevant dimeric arrangements on the TiO(2) surface and evaluating, at the same time, the associated spectroscopic response, an almost quantitative description of the extremely different aggregation behavior of the two dyes is provided. Nicely reproducing the experimental evidence, the present results predict strong aggregation interactions and a sizable red-shift of the absorption band in the case of D102, while negligible effects for D149. Our results open the possibility of computationally screening the various aggregation patterns and predicting the corresponding optical response, thus paving the way to an effective molecular engineering of further enhanced sensitizers for solar cell applications.