**3. Conclusion**

The redox reaction of dicyanobis(2,2′-dipyridyl)iron(III)-iodide and dicyanobis(1,10-phenanthroline)iron(III)-iodide could be used to improve the stability and efficiency of dye-sensitized solar cells. The proposed sensitizer-mediator interaction could be both cost-effective and ecologically advantageous due to the low cost of photosensitive iron complexes. To catalyze the indicated sensitizer-mediator processes in aqueous medium, a modest amount (10 volume percent) of organic solvent, such as tertiary butyl alcohol and 1,4-dioxane, can be utilized. Both solvents are relatively benign to the environment and inert to involvement in the redox process, so they do not cause parallel reactions or complex kinetics. In contrast to dicyanobis(2,2′-dipyridyl)iron(III)-iodide, which follows first order, tertiary butyl alcohol catalyzes the reaction of dicyanobis(1,10-phenanthroline)iron(III)-iodide to third order. Both reactions have rates that are independent of the concentration of oxidizing agents (potential sensitizers), emphasizing the need to use such oxidants in DSSCs to control a reaction that is solely dependent on the concentration of the reductant/reducing agent (mediator). Such sensitizer-mediator interactions are simple to manage, and the rate of reaction can be sped up or slowed down by adjusting the concentration of just one reactant. Furthermore, the rate of reaction was enhanced several times faster by using 1,4-dioxane instead of tertiary butyl alcohol, which may be useful in the recombination process in DSSCs. The inter-nuclear distances for the bpy-TBA and phen-TBA systems were 130 and 53 pm, respectively. However, with the bpy-dioxane and phen-TBA systems, it was 59 and 53 pm, respectively. These findings pertain to solvent catalysis by reducing inter-nuclear distances, resulting in a rapid electron transfer process. This research/study contributes to the development of a cost-effective and environmentally friendly strategy for improving the stability and efficiency of DSSCs.

*Solvent Catalysis in the Sensitizer-Mediator Redox Kinetics DOI: http://dx.doi.org/10.5772/intechopen.105393*
