Electron-phonon coupling in organic semiconductors

Open Access
Authors
  • L. Di Virgilio
Supervisors
Cosupervisors
  • H.I. Wang
Award date 18-11-2024
ISBN
  • 9783949783142
Number of pages 131
Organisations
  • Faculty of Science (FNWI) - Institute of Physics (IoP)
Abstract
This thesis investigates the charge transport in organic semiconductors using terahertz (THz) spectroscopy. The flexible nature and the optoelectronic properties of organic semiconductors make them excellent candidates for the next generation of flexible conductive materials. However, their electronic mobility remains lower than inorganic semiconductors, due to the relatively weak intermolecular electronic coupling and strong electron-vibration interactions originating from their soft and disordered structure. The recent developments in polymer chemistry have enabled the synthesis of small molecular crystalline organic semiconductors, with a mobility reaching approximately 10 cm2/Vs. These values are higher than the charge mobility observed in conventional polymers (approximately 1 cm2/Vs). Our temperature-dependent measurements conducted on two small molecular semiconductors (DNTT and its alkylated derivative, C8-DNTT-C8), revealed that charges undergo transient localization due to the large motion of their soft lattice. The scattering of charges with low-frequency vibrations around 10 meV and 16 meV limits the conductivity of DNTT and C8-DNTT-C8, respectively. Understanding the factors that limit electron mobility in these systems allows for better semiconductor design to enhance their electrical performance. In the same material system, we have also investigated how the interaction between electron-hole pairs and vibrations affects their optical and optoelectronic properties. Finally, we explored an alternative approach to control conductivity by cavity. In this designed experiment, we measured the photoresponse of an inorganic-organic semiconductor perovskite whose THz vibrations were coupled with a THz cavity. Despite the apparent polariton formation under strong electron-phonon coupling, the cavity-coupled material properties remained unaffected. By tuning the interaction between the cavity and the phonon, the terahertz response of the integral perovskite-cavity system can be modulated, offering potential benefits for integrated photonic devices.
In conclusion, our findings provide insights into the control and understanding of electron-phonon coupling in organic semiconductors.
Document type PhD thesis
Note Chapter 3: This is the peer reviewed version of the following article: Z. Y. Wang, L. Di Virgilio, Z. F. Yao, Z. D. Yu, X. Y. Wang, Y. Y. Zhou, Q. Y. Li, Y. Lu, L. Zou, H. I. Wang, X. Y. Wang, J. Y. Wang, and J. Pei, “Correlating charge transport properties of conjugated polymers in solution aggregates and thinfilm aggregates,” Angewandte Chemie International Edition, vol. 60, no. 37, pp. 20483–20488, 2021, which has been published in final form at https://doi.org/10.1002/anie.202107395. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.
Language English
Other links https://doi.org/10.1002/anie.202107395
Downloads
Thesis (complete) (Embargo up to 2026-11-18)
Chapter 2: THz time-domain spectroscopy (Embargo up to 2026-11-18)
Chapter 5: Exciton-vibrational coupling in the organic semiconductor DNTT (Embargo up to 2026-11-18)
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