Rational design of Co-based redox mediators for dye-sensitized solar cells by density functional theory

Density functional theory (DFT) calculations were carried out to explore the effects of chemically modifying the polypyridine ligands and design efficient Co-based redox mediators for dye-sensitized solar cells (DSSCs). Our results showed that the redox properties of cobalt complexes can be well tuned by altering the number and position of nitrogen atoms on the ligand ring. Adding oxygen atoms on the ligand ring will evidently increase the redox potential, which might be unfavorable for the dye regeneration. The designed good redox mediators possess similar redox potential and reorganization energy to the current high-efficiency redox couples, thus are promising to be used in prospective DSSCs.