Electroluminescence from a phthalocyanine monolayer encapsulated in a van der Waals tunnel diode

James, Tyler; Bradford, Jonathan; Kerfoot, James; Korolkov, Vladimir V.; Alkhamisi, Manal; Taniguchi, Takashi; Watanabe, Kenji; Nizovtsev, Anton S.; Antolín, Elisa; Besley, Elena; Svatek, Simon A.; Beton, Peter H.

Abstract

Monolayers of free base phthalocyanine (H2Pc) are grown on monolayer and few-layer exfoliated flakes of hexagonal 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 H2Pc monolayer is sandwiched 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 excited resulting in the emission of photons with wavelengths which are close to the peaks observed in photoluminescence. We also observe electroluminescence at voltages where the energy 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 triplet state. Our results provide insights into the differences in excitation and relaxation of molecules 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.

Citation

James, T., Bradford, J., Kerfoot, J., Korolkov, V. V., Alkhamisi, M., Taniguchi, T., …Beton, P. H. (2023). Electroluminescence from a phthalocyanine monolayer encapsulated in a van der Waals tunnel diode. Molecular Physics, 121(7-8), Article e2197081. https://doi.org/10.1080/00268976.2023.2197081

• Journal Article Type: Article
• Acceptance Date: Mar 24, 2023
• Online Publication Date: Apr 13, 2023
• Publication Date: Apr 13, 2023
• Deposit Date: May 19, 2023
• Publicly Available Date: May 19, 2023
• Journal: Molecular Physics
• Print ISSN: 0026-8976
• Electronic ISSN: 1362-3028
• Publisher: Taylor and Francis
• Peer Reviewed: Peer Reviewed
• Volume: 121
• Issue: 7-8
• Article Number: e2197081
• DOI: https://doi.org/10.1080/00268976.2023.2197081
• Keywords: Phthalocyanine; electroluminescence; van der Waals heterostructure; two dimensional molecular self assembly
• Public URL: https://nottingham-repository.worktribe.com/output/19465536
• Publisher URL: https://www.tandfonline.com/doi/full/10.1080/00268976.2023.2197081
• Additional Information: Memorial Issue for Nick Besley