Diffraction imaging of nanocrystalline structures in organic semiconductor molecular thin films

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Abstract

The properties of organic solids depend on their structure and morphology, yet direct imaging using conventional electron microscopy methods is hampered by the complex internal structure of these materials and their sensitivity to electron beams. Here, we manage to observe the nanocrystalline structure of two organic molecular thin-film systems using transmission electron microscopy by employing a scanning nanodiffraction method that allows for full access to reciprocal space over the size of a spatially localized probe (~2 nm). The morphologies revealed by this technique vary from grains with pronounced segmentation of the structure—characterized by sharp grain boundaries and overlapping domains—to liquid-crystal structures with crystalline orientations varying smoothly over all possible rotations that contain disclinations representing singularities in the director field. The results show how structure–property relationships can be visualized in organic systems using techniques previously only available for hard materials such as metals and ceramics.

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Fig. 1: Schematic of the diffraction imaging technique.
Fig. 2: Comparison of grain morphology between DIO samples.
Fig. 3: Comparison of grain morphology between PBTTT samples.
Fig. 4: Autocorrelation of the primary lattice vectors over distance Δr and relative orientation Δθ, for the films characterized in Figs. 2 and 3.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

  1. 1.

    Van Krevelen, D. W. & Te Nijenhuis, K. Properties of Polymers: Their Correlation with Chemical Structure; Their Numerical Estimation and Prediction from Additive Group Contributions (Elsevier, 2009).

  2. 2.

    Wilmer, C. E. et al. Large-scale screening of hypothetical metal–organic frameworks. Nat. Chem. 4, 83–89 (2012).

  3. 3.

    Fratini, S., Ciuchi, S., Mayou, D., de Laissardière, G. T. & Troisi, A. A map of high-mobility molecular semiconductors. Nat. Mater. 16, 998–1002 (2017).

  4. 4.

    Ophus, C. Four dimensional scanning transmission electron microscopy: from scanning nanodiffraction to ptychography and beyond. Microsc. Microanal. 25, 563–582 (2019).

  5. 5.

    Kim, J. H. et al. Optimization and analysis of conjugated polymer side chains for high‐performance organic photovoltaic cells. Adv. Funct. Mater. 26, 1517–1525 (2016).

  6. 6.

    Li, G. et al. High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nat. Mater. 4, 864–868 (2005).

  7. 7.

    Zhao, W. et al. Fullerene‐free polymer solar cells with over 11% efficiency and excellent thermal stability. Adv. Mater. 28, 4734–4739 (2016).

  8. 8.

    Smits, E. C. P. et al. Bottom-up organic integrated circuits. Nature 455, 956–959 (2008).

  9. 9.

    Di, D. et al. Efficient triplet exciton fusion in molecularly doped polymer light‐emitting diodes. Adv. Mater. 29, 1605987 (2017).

  10. 10.

    Salaneck, W. R., Friend, R. H. & Brédas, J. L. Electronic structure of conjugated polymers: consequences of electron–lattice coupling. Phys. Rep. 319, 231–251 (1999).

  11. 11.

    Collini, E. & Scholes, G. D. Coherent intrachain energy migration in a conjugated polymer at room temperature. Science 323, 369–373 (2009).

  12. 12.

    Sirringhaus, H. et al. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature 401, 685–688 (1999).

  13. 13.

    Lemaur, V., Steel, M., Beljonne, D., Brédas, J.-L. & Cornil, J. Photoinduced charge generation and recombination dynamics in model donor/acceptor pairs for organic solar cell applications: a full quantum-chemical treatment. J. Am. Chem. Soc. 127, 6077–6086 (2005).

  14. 14.

    Zhang, L. et al. Poly(3-butylthiophene) inducing crystallization of small molecule donor for enhanced photovoltaic performance. J. Phys. Chem. C 119, 23310–23318 (2015).

  15. 15.

    McCulloch, I. et al. Liquid-crystalline semiconducting polymers with high charge-carrier mobility. Nat. Mater. 5, 328–333 (2006).

  16. 16.

    Takacs, C. J. et al. Mapping orientational order in a bulk heterojunction solar cell with polarization-dependent photoconductive atomic force microscopy. ACS Nano 8, 8141–8151 (2014).

  17. 17.

    Dennler, G., Scharber, M. C. & Brabec, C. J. Polymer‐fullerene bulk‐heterojunction solar cells. Adv. Mater. 21, 1323–1338 (2009).

  18. 18.

    Zhao, W., Li, S., Zhang, S., Liu, X. & Hou, J. Ternary polymer solar cells based on two acceptors and one donor for achieving 12.2% efficiency. Adv. Mater. 29, 1604059 (2017).

  19. 19.

    Maged, A. et al. Toward additive‐free small‐molecule organic solar cells: roles of the donor crystallization pathway and dynamics. Adv. Mater. 27, 7285–7292 (2015).

  20. 20.

    Arca, F., Loch, M. & Lugli, P. Enhancing efficiency of organic bulkheterojunction solar cells by using 1,8-diiodooctane as processing additive. IEEE J. Photovolt. 4, 1560–1565 (2014).

  21. 21.

    Reichenberger, M. et al. Watching paint dry: the impact of diiodooctane on the kinetics of aggregate formation in thin films of poly(3-hexylthiophene). Macromolecules 49, 6420–6430 (2016).

  22. 22.

    Herath, N. et al. Unraveling the fundamental mechanisms of solvent-additive-induced optimization of power conversion efficiencies in organic photovoltaic devices. ACS Appl. Mater. Interfaces 8, 20220–20229 (2016).

  23. 23.

    Van Der Poll, T. S., Love, J. A., Nguyen, T. Q. & Bazan, G. C. Non‐basic high‐performance molecules for solution‐processed organic solar cells. Adv. Mater. 24, 3646–3649 (2012).

  24. 24.

    Brown, S. J. et al. Enhancing organic semiconductor–surface plasmon polariton coupling with molecular orientation. Nano Lett. 17, 6151–6156 (2017).

  25. 25.

    Panova, O. et al. Orientation mapping of semicrystalline polymers using scanning electron nanobeam diffraction. Micron 88, 30–36 (2016).

  26. 26.

    Frank, F. C. I. Liquid crystals. On the theory of liquid crystals. Discuss. Faraday Soc. 25, 19–28 (1958).

  27. 27.

    Meyer, R. B. On the existence of even indexed disclinations in nematic liquid crystals. Philos. Mag. 27, 405–424 (1973).

  28. 28.

    Saupe, A. Disclinations and properties of the directorfield in nematic and cholesteric liquid crystals. Mol. Cryst. Liq. Cryst. 21, 211–238 (2007).

  29. 29.

    Jimison, L. H., Toney, M. F., McCulloch, I., Heeney, M. & Salleo, A. Charge-transport anisotropy due to grain boundaries in directionally crystallized thin films of regioregular poly(3-hexylthiophene). Adv. Mater. 21, 1568–1572 (2009).

  30. 30.

    Merzkirch, W. Flow Visualization (Elsevier, 2012).

  31. 31.

    Wood, B. A. & Thomas, E. L. Are domains in liquid crystalline polymers arrays of disclinations? Nature 324, 655–657 (1986).

  32. 32.

    Collins, B. A. et al. Polarized X-ray scattering reveals non-crystalline orientational ordering in organic films. Nat. Mater. 11, 536–543 (2012).

  33. 33.

    Qian, L. et al. Effect of crystallinity of fullerene derivatives on doping density in the organic bulk heterojunction layer in polymer solar cells. Chin. Phys. Lett. 32, 056801 (2015).

  34. 34.

    Yang, X. et al. Crystalline organization of a methanofullerene as used for plastic solar‐cell applications. Adv. Mater. 16, 802–806 (2004).

  35. 35.

    Takacs, C. J. et al. Remarkable order of a high-performance polymer. Nano Lett. 13, 2522–2527 (2013).

  36. 36.

    Rivnay, J., Mannsfeld, S. C. B., Miller, C. E., Salleo, A. & Toney, M. F. Quantitative determination of organic semiconductor microstructure from the molecular to device scale. Chem. Rev. 112, 5488–5519 (2012).

  37. 37.

    Mollinger, S. A., Krajina, B. A., Noriega, R., Salleo, A. & Spakowitz, A. J. Percolation, tie-molecules, and the microstructural determinants of charge transport in semicrystalline conjugated polymers. ACS Macro Lett. 4, 708–712 (2015).

  38. 38.

    Mohammadi, E. et al. Dynamic-template-directed multiscale assembly for large-area coating of highly-aligned conjugated polymer thin films. Nat. Commun. 8, 16070 (2017).

  39. 39.

    Pekin, T. C., Gammer, C., Ciston, J., Minor, A. M. & Ophus, C. Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping. Ultramicroscopy 176, 170–176 (2017).

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Acknowledgements

Primary funding for the work was provided by the Electron Microscopy of Soft Matter Program from the Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the US Department of Energy under contract no. DE-AC02-05CH11231. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. L.B. and A.S. acknowledge funding from the National Science Foundation DMR Award no. 1808401. The authors also thank H. Yan for providing materials and M. Toney for useful discussions.

Author information

A.M.M. and N.B. conceived of the project. C.J.T., L.B. and O.P. prepared the samples. O.P. and K.C.B. designed the experiment and acquired the data. C.O., O.P., K.C.B., C.J.T., L.B., A.S. and A.M.M, analysed the data and all authors contributed to writing the manuscript.

Correspondence to Andrew M. Minor.

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Panova, O., Ophus, C., Takacs, C.J. et al. Diffraction imaging of nanocrystalline structures in organic semiconductor molecular thin films. Nat. Mater. 18, 860–865 (2019) doi:10.1038/s41563-019-0387-3

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