Enhanced intramolecular charge transfer of organic dyes containing hydantoin donor: A DFT study

As a key factor for promoting electron transfer to the semiconductor, the intramolecular charge transfer (ICT) process in dye-sensitized solar cells (DSSCs) is crucial to enhancing the conversion efficiency. In this study, the effects of anchoring groups on charge transfer during dye excitation and interfacial electron injection from the dyes to the semiconductor were theoretically investigated. The calculation results indicate that the sensitizers with hydantoin anchoring groups, namely HY-4, HY-3, HQ-4, and HQ-3, can significantly adjust the orbital energy levels and increase the HOMO-LUMO energy gaps. Importantly, the ICT process of sensitizers before and after binding TiO2 cluster were detected via frontier molecular orbitals, electronic transition processes and transferred charges on the basis of the excitation (q(CT)), the transferred charge distance (d(CT)) and the dipole moment (mu(CT)). The calculation results confirm that HY-4 and HY-3 greatly improve ICT performances relative to CA-4, which successfully interprets the experimentally observed efficiency difference. Moreover, the inserting acceptor moiety quinoxaline and hydantoin anchoring groups, namely HQ-4 and HQ-3, play an important role in raising the efficiency of ICT process. The finding can promote further understanding of the relationship between structure and performance of organic dyes containing hydantoin anchoring groups, so as to help them become more efficient dyes for DSSCs.