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

Linnea Lindh, Olga Gordivska, Samuel Persson, Hannes Michaels, Hao Fan, Pavel Chábera, Nils W. Rosemann, Arvind Kumar Gupta, Iacopo Benesperi, Jens Uhlig, Om Prakash, Esmaeil Sheibani, Kasper S. Kjaer, Gerrit Boschloo, Arkady Yartsev, Marina Freitag, Reiner Lomoth, Petter Persson, Kenneth Wärnmark

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskriftPeer review

1 Citering (SciVal)

Sammanfattning

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/I3redox 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.

Originalspråkengelska
Sidor (från-till)16035-16053
Antal sidor19
TidskriftChemical Science
Volym12
Utgåva48
DOI
StatusPublished - 2021 dec. 28

Bibliografisk information

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.

Ämnesklassifikation (UKÄ)

  • Fysikalisk kemi
  • Atom- och molekylfysik och optik

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