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Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures

Nature Materials volume 11, pages 788–794 (2012)Cite this article

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Abstract

Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the heterointerfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN2 single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behaviour from room temperature to ~150 K, and remains as high as ~1 cm2 V−1 s−1 at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively on the basis of the heterostructure band diagram. These results elucidate the electronic structure of rubrene/PDIF-CN2 interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors.

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Figure 1: Rubrene–PDIF-CN2 Schottky-gated heterostructures.
Figure 2: Characterization of the Schottky gate.
Figure 3: In-plane transport characteristics of Schottky-gated rubrene/PDIF-CN2 interfaces.
Figure 4: Temperature dependence of electron mobility and density at rubrene/PDIF-CN2 interfaces.
Figure 5: Energy level alignment of organic interfaces and band diagram of rubrene–PDIF-CN2 Schottky-gated heterostructures.

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Acknowledgements

The authors would like to thank C. Caillier for his assistance during the SKFPM measurements and S. Ono, A. Ferreira and I. Crassee for assistance. This study was financially supported by MaNEP, the Swiss National Science Foundation, NEDO and the AFOSR (FA9550-08-01-0331).

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Authors and Affiliations

  1. DPMC and GAP, University of Geneva, 24 quai Ernest Ansermet, CH1211 Geneva, Switzerland

    Ignacio Gutiérrez Lezama, Nikolas A. Minder, Flavia V. Di Girolamo & Alberto F. Morpurgo

  2. CERG, RIKEN Advanced Science Institute, Wako, Saitama 351-0198, Japan

    Masaki Nakano

  3. Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, USA

    Zhihua Chen & Antonio Facchetti

  4. CHEM, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA

    Zhihua Chen & Antonio Facchetti

  5. CNR-SPIN and University of Naples, p.le Tecchio 80 80125 Naples, Italy

    Flavia V. Di Girolamo

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  1. Ignacio Gutiérrez Lezama
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  3. Nikolas A. Minder
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  4. Zhihua Chen
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  5. Flavia V. Di Girolamo
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  6. Antonio Facchetti
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Contributions

I.G.L. developed and fabricated the devices; performed electrical, Hall and SKFPM measurements; analysed the data and interpreted the results. M.N. fabricated and characterized the first un-gated rubrene/PDIF-CN2 charge-transfer interfaces. N.A.M. designed the Hall set-up and contributed to the electrical characterization. F.V.D.G. contributed to the device fabrication and to the electrical measurements. Z.C. and A.F. synthesized and provided the sample material from which the PDIF-CN2 single crystals were grown. A.F. also contributed to the writing of the manuscript. A.F.M. planned and supervised the work, interpreted the results and wrote the manuscript. All authors contributed to the scientific discussion of the results.

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Correspondence to Alberto F. Morpurgo.

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Lezama, I., Nakano, M., Minder, N. et al. Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures. Nature Mater 11, 788–794 (2012). https://doi.org/10.1038/nmat3383

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