134th CEMS Colloquium

Title

Charge, Spin, and Phonon in Organic Semiconductors

Abstract

     The assembly of molecules, in which the molecular orbitals are weakly bound by van der Waals interactions, allows low-cost semiconductor production by solution process near room temperature. The coexistence of “softness” in molecules and semiconductor functionality has led to a foundation of flexible, printed electronics. On the other hand, in organic semiconductors, charges propagate through a slight overlap of molecular orbitals between neighboring molecules, so the transfer integral between adjacent molecules is one order of magnitude smaller than that of inorganic semiconductors. Moreover, in addition to static disorder such as defects, dynamic disorder due to thermal vibration of molecules is extremely large even at room temperature, resulting in the loss of their spatial coherence of electrons. Given that “hardness”, i.e., rigid periodic electrostatic potentials underlie solid-state electronic physics and explain the excellent electronic properties in inorganic semiconductors, the foundation for discussing “softness” in organic semiconductors is indeed fragile.

     Our precise engineering realized that wafer-size single crystals composed of an organic semiconductor layer can be successfully formed via a simple one-shot solution process [1-5]. Particularly in single crystals, it has become possible to correctly evaluate the intrinsic electronic properties, which are not suffered from grain boundaries or defects. Using high-quality single-crystal thin film, we advance our in-depth understanding of correlation between charge, spin and phonon in organic semiconductor [6-9]. In this talk, we briefly summarize the recent progress in printed electronics based on soft organic semiconductors, and address central issues in organic electronics over past half a century; to what extent we can boost the mobility in organic semiconductors? What factor(s) is limiting the mobility in organic semiconductors? How can materials science, synthetic chemistry, and device engineering contribute further developments in organic electronics?

References
[1] A. Yamamura, S. Watanabe, J. Takeya, Sci. Adv. 4, aao5758 (2018).
[2] T. Makita, S. Watanabe, J. Takeya, PNAS. 117, 80 (2019).
[3] S. Kumagai, S. Watanabe, J. Takeya, Sci. Rep. 9, 15897 (2019).
[4] T. Sawada, S. Watanabe, J. Takeya, Nat. Commun. 11, 4839 (2020).
[5] T. Okamoto, S. Watanabe, J. Takeya, Sci. Adv. 6, aaz0632 (2020).
[6] J. Tsurumi, S. Watanabe, J. Takeya, Nat. Phys. 13, 994 (2017).
[7] Y. Yamashita, J. Takeya, S. Watanabe, Nature 572, 634 (2021).
[8] N. Kasuya, S. Watanabe, J. Takeya, Nat. Mater. 20, 1401 (2022).

Contact

email: mnaoko@riken.jp
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