Abstract

Solution-processable perovskite solar cells have recently achieved certified power conversion efficiencies of over 20%, challenging the long-standing perception that high efficiencies must come at high costs. One major bottleneck for increasing the efficiency even further is the lack of suitable hole-transporting materials, which extract positive charges from the active light absorber and transmit them to the electrode. In this work, we present a molecularly engineered hole-transport material with a simple dissymmetric fluorene–dithiophene (FDT) core substituted by N,N-di-p-methoxyphenylamine donor groups, which can be easily modified, providing the blueprint for a family of potentially low-cost hole-transport materials. We use FDT on state-of-the-art devices and achieve power conversion efficiencies of 20.2% which compare favourably with control devices with 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD). Thus, this new hole transporter has the potential to replace spiro-OMeTAD.

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Acknowledgements

This work was supported by the European Union Seventh Framework Programme [FP7/2007–2013] under grant agreement no 604032 of the MESO project, (FP7/2007–2013) ENERGY.2012.10.2.1; NANOMATCELL, grant agreement no. 308997. M.K.N. acknowledges funding by the Swiss National Science Foundation under NRP 70, grant No: 407040_154056, and MG Nanotera. We thank A. Wakamiya, Institute for Chemical Research, Kyoto University Uji, Kyoto 611-0011, Japan, F. Giordano for experimental help with lithium doping of the TiO2 scaffold, and T. Schmaltz for helpful discussions.

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Affiliations

  1. Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, EPFL VALAIS, Rue de l’industrie 17, CP 440, CH-1951 Sion, Switzerland

    • Michael Saliba
    • , Sadig Aghazada
    • , Peng Gao
    • , Rosario Scopelliti
    •  & Mohammad Khaja Nazeeruddin
  2. Istituto di Scienze e Tecnologie Molecolari del Consiglio Nazionale delle Ricerche, CNR-ISTM, via Golgi 19, I-20133 Milano, Italy

    • Simonetta Orlandi
    • , Marco Cavazzini
    •  & Gianluca Pozzi
  3. Advanced Research Division, Materials Research Laboratory, Panasonic Corporation, 1006 Kadoma, Kadoma City, Osaka 571-8501, Japan

    • Taisuke Matsui
  4. Laboratory for Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1015-Lausanne, Switzerland

    • Juan-Pablo Correa-Baena
    •  & Anders Hagfeldt
  5. Computational Laboratory for Hybrid Organic Photovoltaics (CLHYO), CNR-ISTM, via Elce di Sotto 8, I-06123 Perugia, Italy

    • Edoardo Mosconi
    •  & Filippo De Angelis
  6. Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, PO Box 5825, Qatar

    • Klaus-Hermann Dahmen
  7. Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland

    • Antonio Abate
    •  & Michael Graetzel

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Contributions

M.S. and T.M. conceived and designed the experiments, including fabrication and measurement of the PV devices. M.S. conducted DSC and TGA measurements. S.O., M.C. and G.P. designed and synthesized the FDT hole-transporting material. S.A. and P.G. developed crystals and characterized the FDT. J.-P.C.-B. and A.A. optimized TiO2 photoanodes, the perovskite films and characterized SEM. E.M. and F.D.A. performed first-principles calculations. R.S. analysed single crystals. M.S. wrote the first draft of the paper. All the authors contributed to the discussion and the writing of the paper, and approved. M.K.N. directed the scientific research for this work.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Mohammad Khaja Nazeeruddin.

Supplementary information

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    Supplementary Information

    Supplementary Notes 1-3, Supplementary Figures 1-14, Supplementary Tables 1-6, Supplementary References.

Crystallographic information files

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    Supplementary Data

    Crystallographic data for compound FDT.

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DOI

https://doi.org/10.1038/nenergy.2015.17