Tetracoordinated Bis-phenanthroline Copper-Complex Couple as Efficient Redox Mediators for Dye Solar Cells

• Published in: Inorganic chemistry Vol. 55; no. 11; pp. 5245 - 5253
• Main Authors: Magni, Mirko, Giannuzzi, Roberto, Colombo, Alessia, Cipolla, Maria Pia, Dragonetti, Claudia, Caramori, Stefano, Carli, Stefano, Grisorio, Roberto, Suranna, Gian Paolo, Bignozzi, Carlo Alberto, Roberto, Dominique, Manca, Michele
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.06.2016
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.6b00204

A tetracoordinated redox couple, made by [Cu­(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2]­[PF6], 1, and its Cu­(II) form [Cu­(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2]­[PF6]2, 2, has been synthesized, and its electrochemical and photochemical features have been investigated and compared with those of a previously published Cu2+/Cu+ redox shuttle, namely, [Cu­(2,9-dimethyl-1,10-phenanthroline)2]­[PF6], 3, and its pentacoordinated oxidized form [Cu­(2,9-dimethyl-1,10-phenanthroline)2Cl]­[PF6], 4. The detrimental effect of the fifth Cl– ancillary ligand on the charge transfer kinetics of the redox shuttles has been exhaustively demonstrated. Appropriately balanced Cu-based electrolytes have been then formulated and tested in dye solar cells in combination with a π-extended benzothiadiazole dye. The bis-phenanthroline Cu-complexes, 1 and 2, have been found to provide an overall 4.4% solar energy conversion efficiency, which is more than twice that of the literature benchmark couple, 3 and 4, employing a Cl-coordinated oxidized species and even comparable with the performances of a I–/I3 – electrolyte of analogous concentration. A fast counter-electrode reaction, due to the excellent electrochemical reversibility of 2, and a high electron collection efficiency, allowed through the efficient dye regeneration kinetics exerted by 1, represents two major characteristics of these copper-based electron mediators and may constitute a pivotal step toward the development of a next generation of copper-based efficient iodine-free redox shuttles.