Density functional study of alkylpyridine–iodine interaction and its implications in the open-circuit photovoltage of dye-sensitized solar cell

A density functional theory (DFT) method was used to study the monomer and intermolecular charge-transfer complexes of 22 different alkylpyridines with diiodine. DFT calculations revealed that the σ* orbital of iodine interacts with the nitrogen lone pair in pyridines. The open-circuit photovoltage (V_oc) values 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 using alkylpyridines additive were compared to computational calculations on the interaction between pyridines and I₂ by a DFT method. The optimized geometries, frequency analyses, Mulliken population analyses, and interaction energies suggest that the V_oc value of the solar cell is higher, the more alkylpyridine complexes with I₂.