Molecular modeling of 4-methylphthalonitrile for dye sensitized solar cells using quantum chemical calculations.

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 4-methylphthalonitrile was studied based on Hartree-Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectrum was investigated by time dependent-density functional theory (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π→π* transitions. Calculated results suggest that three lowest energy excited states of 4-methylphthalonitrile are due to photo induced electron transfer processes. The interfacial electron transfer between semiconductor TiO₂ electrode and dye sensitizer 4-methylphthalonitrile is due to an electron injection process from excited dye to the semiconductor's conduction band. The role of cyanine and methyl group in 4-methylphthalonitrile in geometries, electronic structures, and spectral properties were analyzed.