Recent Advances of Cobalt(II/III) Redox Couples for Dye-Sensitized Solar Cell Applications

In recent years dye‐sensitized solar cells (DSSCs) have emerged as one of the alternatives for the global energy crisis. DSSCs have achieved a certified efficiency of >11% by using the I−/I3− redox couple. In order to commercialize the technology almost all components of the device have to be improved. Among the various components of DSSCs, the redox couple that regenerates the oxidized sensitizer plays a crucial role in achieving high efficiency and durability of the cell. However, the I−/I3− redox couple has certain limitations such as the absorption of triiodide up to 430 nm and the volatile nature of iodine, which also corrodes the silver‐based current collectors. These limitations are obstructing the commercialization of this technology. For this reason, one has to identify alternative redox couples. In this regard, the Co(II/III) redox couple is found to be the best alternative to the existing I−/I3− redox couple. Recently, DSSC test cell efficiency has risen up to 13% by using the cobalt redox couple. This review emphasizes the recent development of Co(II/III) redox couples for DSSC applications. Dye‐sensitized solar cells have attracted considerable attention due to their high efficiency, low cost and ease of fabrication. The redox couple is one of the essential components in achieving high efficiency and durability of the device. A widely used redox couple is I−/I3−, either in liquid or gel form. However, this has certain constraints, such as corrosion of the platinum back electrode, absorption in the visible region, and a large mismatch between its oxidation potential and that of the sensitizer. Co(II/III) systems are the best alternative redox couples for DSSC applications. This review covers recent advances in the design of various Co(II/III) complexes based on polypyridyl ligands and their applications to DSSCs.