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The beneficial effects of trifluoromethyl-substituents on the photoconversion efficiency of copper(I) dyes in dye-sensitized solar cells

Brunner, F. and Klein, Y. Maximilian and Keller, Sarah and Morris, Collin D. and Prescimone, Alessandro and Constable, Edwin C. and Housecroft, Catherine E.. (2015) The beneficial effects of trifluoromethyl-substituents on the photoconversion efficiency of copper(I) dyes in dye-sensitized solar cells. RSC advances, 5. pp. 58694-58703.

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Abstract

The synthesis and characterization of [Cu(2)2][PF6] and [Cu(3)2][PF6] in which 2 1/4 6,60-bis(trifluoromethyl)- 2,20-bipyridine and 3 1/4 6-trifluoromethyl-2,20-bipyridine are reported. The single crystal structure of [Cu(2)2][PF6] confirms that the copper(I) centre is sterically protected by the four CF3 groups in a near regular tetrahedral environment. The Cu+/Cu2+ oxidation potential is shifted from +0.44 to +0.72 V on going from [Cu(1)2][PF6] to [Cu(2)2][PF6] (1 1/4 6,60-dimethyl-2,20-bipyridine), in keeping with the electronwithdrawing effects of the CF3 groups. 1H and 19F NMR spectroscopic data for a CH2Cl2 solution containing [Cu(1)2][PF6] and [Cu(2)2][PF6] demonstrate that the ligands in [Cu(2)2][PF6] remain highly labile. An on-surface procedure was used to assemble the dyes [Cu(4)(2)]+ and [Cu(4)(3)]+ (4 1/4 anchoring ligand ((6,60-dimethyl-[2,20-bipyridine]-4,40-diyl)bis(4,1-phenylene))bis(phosphonic acid)) on TiO2; solid-state adsorption spectra show that dye coverage for [Cu(4)(3)][PF6] exceeds that of [Cu(4)(2)]- [PF6]. The performances of the dyes in dye-sensitized solar cells (DSCs) are compared with that of [Cu(4)(1)]+. DSCs containing the fluorinated ancillary ligands exhibit photoconversion efficiencies of z30–34% relative to N719 set at 100%; this is a significant enhancement with respect to DSCs containing [Cu(4)(1)]+ with no fluoro-groups. Density functional theory (DFT) calculations for the heteroleptic dyes demonstrate that the HOMO is stabilized upon introduction of the CF3 groups, but that the compositions of the molecular orbitals in the HOMO–LUMO manifold are little changed. The improved DSC performance is associated with enhanced short-circuit current density (JSC) for [Cu(4)(3)]+ and [Cu(4)(2)]+ versus [Cu(4)(1)]+; this is also seen in high EQEmax values of 46% for [Cu(4)(2)]+ and 51% for [Cu(4)(3)]+ (both at lmax 1/4 480 nm).
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Constable)
05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Housecroft)
UniBasel Contributors:Housecroft, Catherine Elizabeth and Constable, Edwin Charles and Brunner, Fabian and Prescimone, Alessandro and Klein, Maximilian and Keller, Sarah and Morris, Collin
Item Type:Article, refereed
Article Subtype:Research Article
Bibsysno:Link to catalogue
Publisher:Royal Society of Chemistry
ISSN:2046-2069
Note:Publication type according to Uni Basel Research Database: Journal article
Language:English
Identification Number:
Last Modified:31 Dec 2015 10:58
Deposited On:04 Sep 2015 14:30

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