Abstract
In dye-sensitized solar cells (DSSCs), the redox mediator in the electrolyte is responsible for the charge transfer within the solar device allowing the regeneration of the dye during the cycle of operation. In this work, complexes of Cu(I) and Cu(II) of chemical composition Cu(dmdpp)2 1+/2+ (dmdpp = 2,9-dimethyl-4,7- diphenyl-1,10-phenanthroline) were synthesized and spectroscopically characterized, and further used as redox couples in assembled DSSC devices. Various sensitizing organic dyes such as D35, Y123 and Y123/XY1b were investigated with the electrolyte Cu(dmdpp)2 1+/2+ resulting in efficiencies of power conversion (PCE, 1000 W m-2 illumination, and AM 1.5G) of 1.57, 1.52, and 1.54 %, respectively. Differences in short-circuit currents obtained from the integration of the incident photon-to-current efficiency (IPCE) spectra and from density-voltage (J-V) curves were observed, probably because of the mass transport limitations in the diffusion of the redox pair in solution, which is likely associated with the larger size of the dmdpp ligand. Transient photovoltage measurements yield shorter electron lifetimes when the complex Cu(dmdpp)2 1+/2+ was incorporated in devices with the Y123 dye in comparison to D35 and Y123/XY1b dye, accounting for the lower open-circuit voltage (VOC) in comparison to D35 and Y123/XY1b.