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Exciton dispersion in two-dimensional organic perylene crystal indicates substantial charge-transfer exciton coupling
IFW Dresden, Germany.
IFW Dresden, Germany.
Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.
Linköping University, Department of Science and Technology, Laboratory of Organic Electronics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-9879-3915
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2023 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 11, article id 115201Article in journal (Refereed) Published
Abstract [en]

Two-dimensional, high-quality perylene single crystals were grown with a space-confined strategy method. The grown films crystallize in the alpha form, as is confirmed by a combination of techniques. Polarization -dependent optical absorption measurements show a strong anisotropy in very good agreement with the literature data, and the anisotropic mobility data in field-effect transistors document the very high crystalline order. Momentum-dependent studies using electron energy-loss spectroscopy reveal a negative dispersion of the first exciton along the crystal b direction with an exciton bandwidth of 72 meV. We argue that this behavior is a result of charge-transfer exciton coupling between the perylene dimers in the unit cell.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2023. Vol. 107, no 11, article id 115201
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-192671DOI: 10.1103/PhysRevB.107.115201ISI: 000946114400002OAI: oai:DiVA.org:liu-192671DiVA, id: diva2:1746425
Note

Funding Agencies|Deutsche Forschungsgemeinschaft [KN393/25, KN393/26]; Swedish Research Council [2016-05498, 2016-05990, 2020-04538, 2018-06048]; Swedish Foundation for Strategic Research [ITM17-0432]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

Available from: 2023-03-28 Created: 2023-03-28 Last updated: 2023-04-17
In thesis
1. Revealing Electronic Structures of 2D Molecular Crystals and Correlating Them with Optoelectronic Properties
Open this publication in new window or tab >>Revealing Electronic Structures of 2D Molecular Crystals and Correlating Them with Optoelectronic Properties
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electronic band structure serves as the foundation for understanding the physics of semiconductors. The electronic band structure of inorganic semiconductors has been well understood based on ideal single crystal samples, thus actually laid the foundation for the prospering development of inorganic semiconductor devices.

As for organic semiconductors, which are currently being pervasive in our daily life, however, the ‘physics’ of organic semiconductors is still far from complete understanding compared to their inorganic counter-parts which could hinder the rapid development of organic electronics. Only few organic single crystals (e.g., rubrene, pentacene) have been well investigated to probe the electronic structure and their relationship with their electrical properties, sufficient experimental evidence is still lacking for intrinsic properties of organic single crystal, which mainly hindered by the limited crystal size and low conductivity.

Two-dimensional molecular crystals (2DMCs) of organic semiconductors are intriguing materials because their unique advantages, such as long-range molecular packing, low defect density and lack of grain boundaries, make 2DMCs an ideal platform for exploring the structure-property relationship, revealing the intrinsic properties and probable carrier transport mechanism, fabricating high-performance optoelectronic devices. Especially, unique optoelectronic properties exhibited in 2DMCs are not found in their bulk counterparts. With breakthrough in crystal engineering for producing large-area (e.g., millimeter or centi-meter even wafer-sized) 2DMCs and material engineering for designing novel organic semiconductors (e.g., C10-DNTT, C6-DPA), all provide a great opportunity to explore the physical origin behind the novel optoelectronic properties of kinds of organic semiconductors and their correlation with optoelectronic device performance, which further guiding material design and facilitating flourishing of organic electronics.

The aim of this thesis is to investigate the electronic structure of 2DMCs and correlate them with their optoelectronic properties. The 2DMCs were mainly produced by space-confined strategy and layer-defining strategy, the produced 2DMCs could be transferred to any substrates for further characterization. One of selected organic materials is 2,6-Bis(4-hexylphenyl)anthracene (C6-DPA), which belongs to anthracene derivates family, typically known for their high luminescence efficiency and carrier mobility. All characterized 2DMCs of C6-DPA show a high quality. Firstly, we fabricated integrated organic effect field transistors e.g., organic phototransistors, organic memory phototransistors based on 2DMCs of C6-DPA to elucidate the high performance and potential applications. To clarify the physical origin of opto-electronic properties, some advanced surface science experimental techniques were used to determine the electronic structure of 2DMCs of C6-DPA. Resonant photoemission spectroscopy reveals a room temperature band dispersion of C6-DPA, which is well explained by calculated band structure. Angle-resolved photoemission spectroscopy results confirm the room temperature dispersion and exhibit anisotropic band dispersion in plane. The anisotropic charge carrier mobility is 2 in plane, where the highest mobility obtained along the molecular direction with obvious band dispersion, suggesting the electronic property and electrical property quite match well. We then investigated the in-fluence of degree of crystallinity on electronic structure by ultraviolet photoemission spectroscopy, all results indicate that high crystallinity help to overcome Coulomb interaction and facilities charge to be delocalized on whole 2D crystal, while in verse in less degree of thin film. We then selected perylene as the second material to explore the exciton band structure by electron energy-loss spectroscopy. The observed negative band dispersion is rationalized by effective inter-dimer coupling with an additional charge transfer contribution. This result could provide guidance for understanding the in-plane charge transport properties in 2D crystal of perylene.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2023. p. 78
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2306
Keywords
2D molecular crystals, Crystal engineering, Electronic structure, Organic field effect transistors
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-193112 (URN)10.3384/9789180751339 (DOI)9789180751322 (ISBN)9789180751339 (ISBN)
Public defence
2023-05-17, K1, Kåkenhus, Campus Norrköping, Norrköping, 10:15 (English)
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Available from: 2023-04-17 Created: 2023-04-17 Last updated: 2023-05-17Bibliographically approved

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Wang, QingqingFahlman, MatsLiu, Xianjie
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