Electrochemical Properties of Cu(II/I)-Based Redox Mediators for Dye-Sensitized Solar Cells

•The electrocatalytic activity of graphene-based catalysts is outperforming that of platinum for the Cu(II/I) redox mediators.•The charge-transfer kinetics and the diffusion rate significantly slowdown in the presence 4-tert-butylpyridine.•Electrochemically clean Cu(II)-bipyridine complexes are prepared by electrochemical oxidation of the parent Cu(I) complexes.

Three Cu(II/I)-phenanthroline and Cu(II/I)-bipyridine redox mediators are studied on various electrodes and in variety of electrolyte solutions using cyclic voltammetry and impedance spectroscopy on symmetrical dummy cells. Graphene-based catalysts provide comparably high activity to PEDOT, and both catalysts outperform the activity of platinum. The charge-transfer kinetics and the diffusion rate significantly slowdown in the presence 4-tert-butylpyridine. This effect is specific only for Cu-mediators (is missing for Co-mediators), and is ascribed to a sensitivity of the coordination sphere of the Cu(II)-species to structural and substitutional changes. The ‘Zombie Cells’ made from symmetrical PEDOT/PEDOT devices exhibit enhanced charge-transfer rate and enhanced diffusion resistance. Electrochemically clean Cu(II)-bipyridine species are prepared, for the first time, by electrochemical oxidation of the parent Cu(I) complexes. Our preparative electrolysis brings numerous advantages over the standard chemical syntheses of the Cu(II)-bipyridine complexes. The superior performance of electrochemically-grown clean Cu(II)-bipyridine complex is demonstrated on practical dye-sensitized solar cells.

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