Exciton Binding Energy in Organic Polymers: Experimental Considerations and Tuning Prospects

Somayeh Kashani, Jeromy James Rech, Tuo Liu, Kyle Baustert, Abbas Ghaffari, Indunil Angunawela, Yuan Xiong, Abay Dinku, Wei You, Kenneth Graham, Harald Ade

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Discrepancies in reported values of exciton binding energy (Eb) for organic semiconductors (OSs) necessitate a comprehensive study. Traditionally, Eb is defined as the difference between the transport gap (Et) and the optical gap (Eopt). Here, the Eb values of PBnDT-TAZ polymer variants are determined using two commonly employed methods: a combination of ultraviolet photoemission spectroscopy and low-energy inverse photoemission spectroscopy (UPS-LEIPS) and solid-state cyclic voltammetry (CV). Eb values obtained by UPS-LEIPS show low dispersion and no clear correlation with the polymer structure and thedielectric properties. In contrast, CV reveals a larger dispersion (200 meV-1 eV) and an apparent qualitative Eb-molecular structure correlation, as the lowest Eb values are observed for oligo-ethylene glycol side chains. This discrepancy is discussed by examining the implications of the traditional definition of Eb. Additionally, the impact of both intrinsic and extrinsic factors contributing to the derived experimental values of Et is discussed. The differences in intrinsic and extrinsic factors highlight the context-dependent nature of measurement when drawing global conclusions. Notably, the observed Eb trend derived from CV is not intrinsic to the pure materials but likely linked to electrolyte swelling and associated changes in dielectric environment, suggesting that high-efficiency single-material organic photovoltaics with low Eb may be possible via high dielectric materials.

Original languageEnglish
Article number2302837
JournalAdvanced Energy Materials
Volume14
Issue number6
DOIs
StatePublished - Feb 9 2024

Bibliographical note

Publisher Copyright:
© 2023 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH.

Keywords

  • cyclic voltammetry
  • exciton binding energy
  • organic semiconductors
  • transport gap
  • ultraviolet photoemission spectroscopy and low-energy inverse photoemission spectroscopy

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Materials Science

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