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Spontaneous formation of metastable orientation with well-organized permanent dipole moment in organic glassy films

Abstract

The performance of organic optoelectronic and energy-harvesting devices is largely determined by the molecular orientation and resultant permanent dipole moment, yet this property is difficult to control during film preparation. Here, we demonstrate the active control of dipole direction—that is, vector direction and magnitude—in organic glassy films by physical vapour deposition. An organic glassy film with metastable permanent dipole moment orientation can be obtained by utilizing the small surface free energy of a trifluoromethyl unit and intramolecular permanent dipole moment induced by functional groups. The proposed molecular design rule could pave a way toward the formation of spontaneously polarized organic glassy films, leading to improvement in the performance of organic molecular devices.

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Fig. 1: Giant surface potential of vacuum-deposited films.
Fig. 2: Spontaneous orientation of proposed F-based molecules.
Fig. 3: Orientation of polarization in vacuum-deposited films of F-based molecules.
Fig. 4: Device applications of polar films.

Data availability

Source data are provided with this paper. Additional information is available from the authors on request. Source data are provided with this paper.

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Acknowledgements

The authors thank K. Kusuhara and N. Nakamura of Kyushu University for preparing chemicals and their thermal analysis. The authors also thank H. Fujimoto, H.-W. Mo and K. Nagayoshi from i3-opera for their help with sample fabrication. This work was supported in part by the Programme for Building Regional Innovation Ecosystems of the Ministry of Education, Culture, Sports, Science and Technology, Japan, the Hoso Bunka Foundation and the Japan Society for the Promotion of Science KAKENHI (grant no. JP21K19010).

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Contributions

The project was conceived and designed by M.T. M.T. designed molecules and M.A. synthesized them. H.N. built the experimental set-up for surface potential. M.T. prepared samples and measured their properties. M.T. and H.N. fabricated VPGs. M.T. and H.N. analysed data. All authors contributed to writing the paper and critically commented on the project.

Corresponding authors

Correspondence to Masaki Tanaka, Hajime Nakanotani or Chihaya Adachi.

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Nature Materials thanks Wolfgang Bruetting, Hirohiko Fukagawa and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Synthesis, Supplementary Figs. 1–24, Tables 1–3, Notes 1–3 and references.

Source data

Source Data Fig. 3

Thickness dependence of surface potential.

Source Data Fig. 4

Device performance, including current density–voltage characteristics and output current profiles.

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Tanaka, M., Auffray, M., Nakanotani, H. et al. Spontaneous formation of metastable orientation with well-organized permanent dipole moment in organic glassy films. Nat. Mater. 21, 819–825 (2022). https://doi.org/10.1038/s41563-022-01265-7

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