Issue 33, 2016

Understanding why replacing I3/I by cobalt(ii)/(iii) electrolytes in bis(diimine)copper(i)-based dye-sensitized solar cells improves performance


The performances of dye-sensitized solar cells (DSCs) comprising heteroleptic bis(diimine)copper(I) based dyes combined with either [Co(bpy)3]2+/3+, [Co(phen)3]2+/3+ or I3/I redox mediators (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been evaluated. The copper(I) dyes contain the anchoring ligand ((6,6′-dimethyl-[2,2′-bipyridine]-4,4′-diyl)bis(4,1-phenylene))bis(phosphonic acid), 1, and an ancillary ligand (2, 3 or 4) with a 2,9-dimethyl-1,10-phenanthroline metal-binding domain. Ligands 2 and 3 include imidazole 2′-functionalities with 4-(diphenylamino)phenyl (2) or 4-(bis(4-n-butoxy)phenylamino)phenyl (3) domains; in 4, the phen unit is substituted in the 4,7-positions with hole-transporting 4-(diphenylamino)phenyl groups. The photoconversion efficiency, η, of each of [Cu(1)(2)]+, [Cu(1)(3)]+ and [Cu(1)(4)]+ considerably improves by replacing the I3/I electrolyte by [Co(bpy)3]2+/3+ or [Co(phen)3]2+/3+, and after a change of electrolyte solvent (MeCN to 3-methoxypropionitrile). Due to the faster charge transfer kinetics and more positive redox potential, the cobalt-based electrolytes are superior to the I3/I electrolyte in terms of open-circuit voltage (VOC), short-circuit current (JSC) and η; values of VOC = 594 mV, JSC = 9.58 mA cm−2 and η = 3.69% (relative to η = 7.12% for N719) are achieved for the best performing DSC which contains [Cu(1)(4)]+ and [Co(bpy)3]2+/3+. Corresponding values for [Cu(1)(4)]+ and I3/I DSCs are 570–580 mV, 5.98–6.37 mA cm−2 and 2.43–2.62%. Electrochemical impedance spectroscopy (EIS) has been used to study DSCs with [Cu(1)(4)]+ and the three electrolytes. EIS shows that the DSC with I3/I has the highest recombination resistance, whereas the [Co(phen)3]2+/3+ electrolyte gives the highest chemical capacitance and VOC and, between [Co(bpy)3]2+/3+ and [Co(phen)3]2+/3+, the higher recombination resistance. The [Co(phen)3]2+/3+ electrolyte exhibits the highest mass transport restrictions which result in a lower JSC and DSC efficiency compared to the [Co(bpy)3]2+/3+ electrolyte.

Graphical abstract: Understanding why replacing I3−/I− by cobalt(ii)/(iii) electrolytes in bis(diimine)copper(i)-based dye-sensitized solar cells improves performance

Supplementary files

Article information

Article type
10 Jun 2016
31 Jul 2016
First published
08 Aug 2016
This article is Open Access
Creative Commons BY license

J. Mater. Chem. A, 2016,4, 12995-13004

Author version available

Understanding why replacing I3/I by cobalt(II)/(III) electrolytes in bis(diimine)copper(I)-based dye-sensitized solar cells improves performance

S. O. Fürer, B. Bozic-Weber, T. Schefer, C. Wobill, E. C. Constable, C. E. Housecroft and M. Willgert, J. Mater. Chem. A, 2016, 4, 12995 DOI: 10.1039/C6TA04879J

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