Solvent Effects on Intra-/Intermolecular Charge Transfer in Indoloquinoxaline-Based Dyes.

In this work, kinetics and dynamics of the functionality of indoloquinoxaline-based dye-sensitized solar cells (DSSCs), QX22-QX25, were investigated in gas and solvent media. Quantum chemistry properties of the dyes at the excited states show that each moiety of the (D)2-A-π-A system has a specific effect on the photovoltaic properties. Solvent effect analysis shows that among ethanol, toluene, tetrahydrofuran, and methylene dichloride, toluene is the preferred medium for intra-/intermolecular charge transfer, dynamically and kinetically. Moreover, the behavior of the light harvesting efficiency (LHE) and incident photon-to-current efficiency (IPCE) are not similar, due to a strong effect of the Gibbs energy of electron injection on the energy conversion efficiency. Finally, the dye composed of -COOH as the anchoring group and thiophene as the π-spacer is the best candidate to be applied in DSSC due to its better efficiency originated from a lower electrophilicity and electronic chemical potential.