Novel Redox Couples Could Aid Solar Cells

Two research teams have independently created new redox couples—charge-shuttling electrochemical reagent pairs—that offer advantages over the conventional iodide-based redox couple used in dye-sensitized solar cells (DSCs). These cells typically consist of a porous dye-coated titanium dioxide electrode and a counter electrode bathed in an electrolyte solution containing the iodide/triiodide (I^–/I₃ ^–) redox couple, which mediates the flow of current generated by the cells’ reduction and oxidation reactions. The I^–/I₃ ^– pair is commonly used because DSCs based on that couple exhibit relatively high stability and current-generating efficiency. But the iodide-based system is corrosive to some materials, such as silver, under consideration for commercial DSC use. In addition, I₃ ^– absorbs a portion of the visible spectrum, reducing DSC efficiency. The two newly described redox couples sidestep those problems. Tina C. Li, Joseph T. Hupp, and coworkers at Northwestern University developed Ni(IV)/Ni(III) bisdicarbollides as a potential iodide-couple replacement (J. Am. Chem. Soc. 2010, 132, 4580). And Mingkui Wang and Michael Grätzel of the Swiss Federal Institute of Technology, Lausanne, and coworkers developed a disulfide-thiolate redox couple based on a 5-mercapto-1-methyltetrazole dimer and its monomer anion (Nat. Chem., DOI: 10.1038/nchem.610).