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Phthalocyanine monolayers are grown on monolayer and few-layer exfoliated flakes of hexag-onal boron nitride (hBN) which are subsequently integrated into a van der Waals tunnel diode. This heterostructure consists of two thin hBN flakes between which the Pc monolayer is sand-wiched and also incorporates upper and lower few layer graphene contacts. When a voltage is applied between the contacts, a tunnel current flows and the embedded molecules can be ex-cited resulting in the emission of photons with wavelengths which are close to the peaks ob-served in photoluminescence. We also observe electroluminescence at voltages where the en-ergy gained by a tunnelling electron is lower than the energy of the emitted photon implying a multi-electron excitation pathway which we attribute to the formation of an intermediate tri-plet state. Our results provide insights into the differences in excitation and relaxation of mole-cules in supramolecular monolayers and bulk crystals and we discuss how the alignment of the energy levels of the molecules and contact layers determine the emission process.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Phthalocyanine, hexagonal boron nitride, electroluminescence

Date published: 2023-04-18

Publisher: Informa UK Limited

Journal:

• Molecular Physics (ISSN: 00268976) vol. 121 issue. 7-8 e2197081

Funding:

• Engineering and Physical Sciences Research Council EP/N033906/1
• Japan Society for the Promotion of Science grant numbers 19H05790, 20H00354 and 21H05233
• The Leverhulme Trust RF2019-460

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1080/00268976.2023.2197081

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Updated at: 2025-02-14 16:30:38 +0900

Published on MDR: 2025-02-14 16:30:38 +0900