Effect of capping ligands and TiO2 supporting on the optical properties of a (CdSe)13 cluster.

The influence of different aliphatic and aromatic ligand molecules on the electronic properties of CdSe quantum dots (QDs) has been examined by employing density functional theory (DFT). Optical spectra were simulated with the real-time time-dependent DFT (RT-TDDFT) methodology. The assignment of the first absorption peak features that occur in these spectra was done by taking into account the composition of the frontier molecular orbitals (MOs) of the different systems. While the aliphatic ligands considered-amine, thiol, and phospine oxides-did not show any major influence on the electronic absorption spectra, some of the aromatic ligands do have a noticeable impact on the optoelectronic properties of the QD. Aromatic ligands are mainly aniline-type molecules; additionally, a thiophenol and uracil were employed to saturate the dangling bonds on the Cd atoms. Finally, a more realistic model of a QD-sensitized solar cell consisting of methylamine-capped (CdSe)13 cluster linked to a TiO2 nanoparticle through a mercaptopropionate bridge was considered. The simulations again show that the lowest electronic excitation takes place within the QD subunit, demonstrating the indirect nature of the electron injection mechanism operating in these solar cells.