Simulation of the Electrochemical Properties of Dye-Sensitized Solar Cells Based on Quinoxaline Dyes: Effects of Hydroxyl Group Numbers and Positions

Twelve various quinoxaline derivative dyes, so coded from Q_1–1 to Q_1–12, have been investigated as sensitizers in dye-sensitized solar cells (DSSCs). The simulation study has been performed using the density functional theory and time dependent (TD–DFT) methods. All derivatives have the same backbone structures, with two oxygens in fixed positions, and varying numbers and/or positions of hydroxyl groups. The TD–DFT calculations have been soundly useful to predict various dye excitation energies and absorption spectra. The influence of varying numbers and positions of oxygen atoms and hydroxyl groups on optical properties for the free dyes has been studied. With such variation, DSSC characteristics such as light-harvesting efficiency (LHE), electronic injection driving force (ΔG_inj) and dye regeneration spontaneity (ΔG_reg) have all been studied. Among the series, the Q_1–7@ ZnTiO₃ interface shows the highest (ΔG_inj) (−2.829 eV) and LHE (0.677). The results indicate that hydroxyl group (OH) numbers and positions influence the DSSC microscopic properties, and consequently the macroscopic properties such as short circuit current density (J_SC) and open circuit potential (V_OC).