Theoretical Study of Hemicyanine Dye as a Dye-Sensitized Solar Cell Light-Absorbing Material

Abstract

We used first-principles calculations to investigate the photo-induced electron transfer (PIET) process of the hemicyanine-(TiO2)(n), complex ((TiO2)(n)-dye) for n=5, 9, 15. The geometries of the (TiO2)(n)-dye in the ground state were optimized using density functional theory (DFT) and their excited states were investigated using the time-dependent OFT (TDDFT) method. The excited energies, which were calculated using the long-range-corrected functionals, CAM-B3LYP and omega B97X-D, were in good agreement with the experimentally observed values. The wave functions based on DFT were used to calculate the charge transfer integrals by the generalized Mulliken-Hush (GMH) approach. In addition, the photo-induced charge separation rate constant (k(CS)) and charge recombination rate constant (k(CR)) were calculated using Marcus theory. The calculated results showed that there were a cascade of electron transfer channels from the dye into the (TiO2) cluster, which increases the k(CS) value. In contrast, the single channel of charge recombination decreases the k(CR), value, which is negligible compared with k(CS), indicating that electron recombination is not favored.