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Highly efficient photocathodes for dye-sensitized tandem solar cells

Nature Materials volume 9, pages 3135 (2010) | Download Citation

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Abstract

Thin-film dye-sensitized solar cells (DSCs) based on mesoporous semiconductor electrodes are low-cost alternatives to conventional silicon devices1,2. High-efficiency DSCs typically operate as photoanodes (n-DSCs), where photocurrents result from dye-sensitized electron injection into n-type semiconductors. Dye-sensitized photocathodes (p-DSCs) operate in an inverse mode, where dye-excitation is followed by rapid electron transfer from a p-type semiconductor to the dye (dye-sensitized hole injection). Such p-DSCs and n-DSCs can be combined to construct tandem solar cells3 (pn-DSCs) with a theoretical efficiency limitation well beyond that of single-junction DSCs (ref. 4). Nevertheless, the efficiencies of such tandem pn-DSCs have so far been hampered by the poor performance of the available p-DSCs (refs 3, 5–15). Here we show for the first time that p-DSCs can convert absorbed photons to electrons with yields of up to 96%, resulting in a sevenfold increase in energy conversion efficiency compared with previously reported photocathodes7. The donor–acceptor dyes, studied as photocathodic sensitizers, comprise a variable-length oligothiophene bridge, which provides control over the spatial separation of the photogenerated charge carriers. As a result, charge recombination is decelerated by several orders of magnitude and tandem pn-DSCs can be constructed that exceed the efficiency of their individual components.

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Acknowledgements

The authors would like to thank the Victorian Government (Department of Primary Industries, ETIS SERD), the ARC Centre of Excellence for Electromaterials Science (ACES), the German Academic Exchange Service (DAAD-Go8 joint research cooperation scheme) and the International Science Linkage Project CG 100059 (DIISR, Australia) for financial support. Furthermore, they would like to acknowledge the ARC for providing equipment support through LIEF, as well as supporting U.B. with an Australian Research Fellowship. Special thanks also to Monash University for supporting U.B. with a Monash Research Fellowship, as well as JGC Catalysts and Chemicals Ltd, Kitakyushu-Shi (Japan) for providing samples of TiO2 screen-printing paste. We would like to thank the German Federal Ministry of Education and Research (BMBF) for financially supporting our research on organic solar-cell materials in the frame of a joint project (OPEG) and the Alexander von Humboldt Foundation for a grant for A.M. This work was also supported by the German Science Foundation (DFG) in the frame of a Collaborative Research Center (SFB 569). Finally we would also like to thank L. Kane-Maguire for assistance in the manuscript preparation process.

Author information

Author notes

    • P. Bäuerle
    •  & U. Bach

    These authors contributed equally to this work

Affiliations

  1. ARC Centre of Excellence for Electromaterials Science, Department of Materials Engineering, Monash University, Clayton Victoria, 3800, Australia

    • A. Nattestad
    • , Y.-B. Cheng
    •  & U. Bach
  2. ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, AIIM Facility, Innovation Campus, University of Wollongong, New South Wales, 2522, Australia

    • A. J. Mozer
  3. Institute for Organic Chemistry II and Advanced Materials, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany

    • M. K. R. Fischer
    • , A. Mishra
    •  & P. Bäuerle
  4. ARC Centre of Excellence for Electromaterials Science, School of Chemistry, Monash University, Clayton Victoria, 3800, Australia

    • U. Bach

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Contributions

U.B. and P.B. proposed the research with further contributions from A.M. and Y.-B.C. A.N. carried out the photovoltaic characterization, optical analysis and optimized the tandem solar cells under the supervision of U.B. and Y.-B.C. Sensitizing dyes were designed and developed in the group of P.B. M.K.R.F. carried out the molecular orbital calculations. A.J.M. and U.B. executed the transient absorption spectroscopy measurements and interpreted the result. U.B., A.N., A.J.M. and M.K.R.F. were mainly responsible for writing the manuscript, with further inputs from P.B., Y.-B.C. and A.M.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to P. Bäuerle or U. Bach.

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DOI

https://doi.org/10.1038/nmat2588

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