Cu(ii/i) redox couples: potential alternatives to traditional electrolytes for dye-sensitized solar cells

Abstract

The redox shuttle is one of the essential ingredients in dye-sensitized solar cell devices. Though the I⁻/I₃⁻ redox couple has dominated in the last couple of decades, however, due to the loss of open-circuit potential, complementary absorption with a sensitizer and the volatile nature restricts the module development. Metal complexes with variable oxidation states are probable alternative candidates as redox shuttles due to the change in their redox potentials with varying ligands in order to suit different sensitizers. Co(III/II) redox couples using polypyridyl ligands have been widely used in DSSC and have crossed the device efficiency of 14%. However, mass transport constraints and health hazards exist due to the commercialization of technology. Inspired from biological electron transfer reactions, Cu(II/I) redox shuttles have gained much attention as redox couples for DSSC applications in recent years. Particularly in low light conditions, it minimizes mass transport, has a device efficiency greater than 32%, and has potential in Internet of Things (IoT) applications. In this review, recent advancements in the use of Cu(II/I) redox shuttles using polypyridyl ligands for DSSC applications are presented.