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Improving the photoresponse of copper(i) dyes in dye-sensitized solar cells by tuning ancillary and anchoring ligand modules

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posted on 16.06.2017 by Biljana Bozic-Weber, Sven Y. Brauchli, Edwin C. Constable, Sebastian O. Furer, Catherine E. Housecroft, Frederik J. Malzner, Iain Wright, Jennifer A. Zampese
The syntheses of five homoleptic copper(i) complexes [CuL 2][PF6] are described in which L is a 4,4′-di(4- bromophenyl)-6,6′-dialkyl-2,2′-bipyridine ligand (compounds 1-4 with methyl, nbutyl, isobutyl and hexyl substituents, respectively) or 4,4′-di(4-bromophenyl)-6,6′-diphenyl-2,2′- bipyridine (5). The new ligands 2-5 and copper(i) complexes [CuL 2][PF6] (L = 1-5) have been fully characterized. The single crystal structures of 2{[Cu(1)2][PF6]} ·3Me2CO, [Cu(2)2][PF6], 2{[Cu(3) 2][PF6]}·Et2O and [Cu(5) 2][PF6]·CH2Cl2 have been determined. The first three structures show similar distorted tetrahedral environments for the Cu+ ions with angles between the least squares planes of the bpy domains of 85.6, 86.4 and 82.9°, respectively; in contrast, the Cu+ ion in [Cu(5)2][PF6] ·CH2Cl2 is in a flattened coordinate environment due to intra-cation face-to-face π-interactions. The solution absorption spectra of the complexes with ligands 1-4 are virtually identical with an MLCT band with values of λmax = 481-488 nm. In contrast, the absorption spectrum of [Cu(5)2][PF6] shows two broad bands in the visible region. Cyclic voltammetric data show that oxidation of the copper(i) centre occurs at a more positive potential in [Cu(2) 2][PF6], [Cu(3)2][PF6] and [Cu(4)2][PF6] than in [Cu(1)2][PF6] or [Cu(5)2][PF6] with the latter being oxidized at the lowest potential. The complexes have been used to prepare dye-sensitized solar cells (DSCs) incorporating heteroleptic dyes of type [Cu(L)(L anchor)]+ where L is 1-5 and Lanchor is a 6,6′-dimethyl-2,2′-bipyridine functionalized in the 4- and 4′-positions with phosphonic acid groups with (Lanchor = 7) and without (Lanchor = 6) a spacer between the metal-binding and anchoring domains. The presence of the spacer results in enhanced performances of the dyes, and the highest energy conversion efficiencies are observed for the dyes [Cu(3)(7)]+ (η = 2.43% compared to 5.96% for standard dye N719) and [Cu(5)(7)]+ (η = 2.89% compared to 5.96% for N719). Measurements taken periodically over the course of a week indicate that the cells undergo a ripening process (most clearly seen for [Cu(5)(6)]+ and [Cu(5)(7)]+) before their optimum performances are achieved. IPCE (EQE) data are presented and confirm that, although the photo-to-current conversions are promising (37-49% for λmax ≈ 480 nm), the copper(i) dyes do not realize the broad spectral response exhibited by N719. © 2013 The Royal Society of Chemistry.

Funding

We thank the European Research Council (Advanced Grant 267816 LiLo), the Swiss National Science Foundation, the Swiss Nanoscience Institute and the University of Basel for financial support.

History

School

  • Science

Department

  • Chemistry

Published in

Dalton Transactions

Volume

42

Issue

34

Pages

12293 - 12308

Citation

BOZIC-WEBER, B., 2013. Improving the photoresponse of copper(i) dyes in dye-sensitized solar cells by tuning ancillary and anchoring ligand modules. Dalton Transactions, 42(34), pp. 12293-12308.

Publisher

© The Royal Society of Chemistry

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VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2013

Notes

This is an Open Access Article. It is published by Royal Society of Chemistry under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND). Full details of this licence are available at: http://creativecommons.org/licenses/by-nc-nd/4.0/

ISSN

1477-9226

eISSN

1477-9234

Language

en

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