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Dye-sensitized solar cells based on Fe N-heterocyclic carbene photosensitizers with improved rod-like push-pull functionality

Lindh, Linnea LU orcid ; Gordivska, Olga LU ; Persson, Samuel LU ; Michaels, Hannes ; Fan, Hao LU ; Chábera, Pavel LU ; Rosemann, Nils W. LU ; Gupta, Arvind Kumar LU ; Benesperi, Iacopo and Uhlig, Jens LU , et al. (2021) In Chemical Science 12(48). p.16035-16053
Abstract

A new generation of octahedral iron(ii)-N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push-pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well... (More)

A new generation of octahedral iron(ii)-N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push-pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push-pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I−/I3−redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO2. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (<100 fs) interfacial electron injection from the heteroleptic dyes to TiO2. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO2back to the oxidized dye, leaving only 5-10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 μs) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6-8 μs). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.

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published
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Chemical Science
volume
12
issue
48
pages
19 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85121698950
  • pmid:35024126
ISSN
2041-6520
DOI
10.1039/d1sc02963k
language
English
LU publication?
yes
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Funding Information: The authors acknowledge Daniel Strand for his help with SC-XRD measurements and analyses, Edoardo Domenichini for help with interpreting spectroscopy results, Nidhi Kaul for providing data for electrochemistry and spectroelec-trochemistry and Yogesh Goriya for help with synthesis of compounds. The authors would also like to point out the helpful comments and pertinent questions from the referees that contributed to signicantly strengthen this manuscript in the reviewing process. The Swedish Foundation for Strategic Research (SSF) as well as the Knut and Alice Wallenberg (KAW) Foundations are acknowledged for nancial support. KW acknowledges support from the Swedish Research Council (VR), the Swedish Energy Agency (Energimyndigheten), the LMK Foundation, the Carl Trygger Foundation and the Sten K Johnson Foundation. PP acknowledges support from the Swedish Research Council (VR), the Swedish Energy Agency (Energimyndigheten), eSSENCE, and the computing centres LUNARC and NSC through support via SNIC. RL acknowledges support from the Swedish Research Council (VR). GB acknowledges support from the STandUP for Energy program. NWR gratefully acknowledges funding from the Alexander von Humboldt Foundation within the Feodor-Lynen Fellowship program. JU gratefully acknowledges funding from the Swedish Research Council (VR). Funding Information: The authors acknowledge Daniel Strand for his help with SC-XRD measurements and analyses, Edoardo Domenichini for help with interpreting spectroscopy results, Nidhi Kaul for providing data for electrochemistry and spectroelectrochemistry and Yogesh Goriya for help with synthesis of compounds. The authors would also like to point out the helpful comments and pertinent questions from the referees that contributed to significantly strengthen this manuscript in the reviewing process. The Swedish Foundation for Strategic Research (SSF) as well as the Knut and Alice Wallenberg (KAW) Foundations are acknowledged for financial support. KW acknowledges support from the Swedish Research Council (VR), the Swedish Energy Agency (Energimyndigheten), the LMK Foundation, the Carl Trygger Foundation and the Sten K Johnson Foundation. PP acknowledges support from the Swedish Research Council (VR), the Swedish Energy Agency (Energimyndigheten), eSSENCE, and the computing centres LUNARC and NSC through supportviaSNIC. RL acknowledges support from the Swedish Research Council (VR). GB acknowledges support from the STandUP for Energy program. NWR gratefully acknowledges funding from the Alexander von Humboldt Foundation within the Feodor-Lynen Fellowship program. JU gratefully acknowledges funding from the Swedish Research Council (VR). Publisher Copyright: © The Royal Society of Chemistry 2021.
id
1a516220-9324-4819-ac4b-3e414dc02a68
date added to LUP
2022-01-25 08:23:58
date last changed
2024-06-17 03:01:41
@article{1a516220-9324-4819-ac4b-3e414dc02a68,
  abstract     = {{<p>A new generation of octahedral iron(ii)-N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push-pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push-pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I<sup>−</sup>/I<sub>3</sub><sup>−</sup>redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO<sub>2</sub>. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (&lt;100 fs) interfacial electron injection from the heteroleptic dyes to TiO<sub>2</sub>. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO<sub>2</sub>back to the oxidized dye, leaving only 5-10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 μs) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6-8 μs). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.</p>}},
  author       = {{Lindh, Linnea and Gordivska, Olga and Persson, Samuel and Michaels, Hannes and Fan, Hao and Chábera, Pavel and Rosemann, Nils W. and Gupta, Arvind Kumar and Benesperi, Iacopo and Uhlig, Jens and Prakash, Om and Sheibani, Esmaeil and Kjaer, Kasper S. and Boschloo, Gerrit and Yartsev, Arkady and Freitag, Marina and Lomoth, Reiner and Persson, Petter and Wärnmark, Kenneth}},
  issn         = {{2041-6520}},
  language     = {{eng}},
  month        = {{12}},
  number       = {{48}},
  pages        = {{16035--16053}},
  publisher    = {{Royal Society of Chemistry}},
  series       = {{Chemical Science}},
  title        = {{Dye-sensitized solar cells based on Fe N-heterocyclic carbene photosensitizers with improved rod-like push-pull functionality}},
  url          = {{http://dx.doi.org/10.1039/d1sc02963k}},
  doi          = {{10.1039/d1sc02963k}},
  volume       = {{12}},
  year         = {{2021}},
}