Density functional study of imidazole–iodine interaction and its implication in dye-sensitized solar cell

The monomer and charge-transfer complexes of 14 different imidazole derivatives with diiodine were studied by a density functional theory (DFT) method. DFT calculations revealed that the σ* orbital of iodine interacts with the nitrogen lone pair of imidazoles at position 3. The influence of these imidazoles addition on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized nanocrystalline TiO2 solar cell with an I−/I3− redox electrolyte in acetonitrile was also studied. All of the imidazole derivatives enhanced the open-circuit photovoltage (Voc). The resulting Voc values of solar cell were compared to computational calculations on the interaction between imidazoles and I2 by a DFT method. Optimized geometries, frequency analyses, and interaction energies suggest that the Voc value is higher, the more the imidazole complexes with I2.