Using Scanning Electrochemical Microscopy to Examine Copper(I) Sensitizers for Dye-Sensitized Solar Cells

The examination of surface charges within dye-sensitized solar cells containing copper­(I)-based dyes has proved to be difficult due to the instability of these systems compared with existing commercial dyes. We report the use of scanning electrochemical microscopy in a setup in which homoleptic [Cu­(L_ancillary)₂]⁺ complexes are used as the electrolyte to investigate a series of [Cu­(L_anchor)­(L_ancillary)]⁺ sensitizers. The ligands L_anchor and L_ancillary are 6,6′-disubstituted 2,2′-bipyridines. By incorporating sensitizers and electrolytes containing the same ligands, changes in the diffusion layer around the scanning electrode have been used to map the substrate surface both in the dark and under controlled illumination. Examination of the changes in current as a constant potential is applied shows the formation of stable surface charge as the cell components equilibrate. Comparison of the time taken for this stabilization to occur as ancillary or anchoring ligands within the dye and electrolyte are varied shows a significant dependence upon the aliphatic substituents in the 6,6′-positions of the ligands that surround the copper­(I) center.