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Near-edge X-ray absorption fine structure study of the C-60-derivative PCBM
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2013 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 568, 130-134 p.Article in journal (Refereed) Published
Abstract [en]

The fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester plays a key role for electron transport in polymer solar cells. We have studied the unoccupied molecular orbitals of PCBM by near edge X-ray absorption fine structure spectroscopy and were able to assign the main resonances to molecular moieties by comparison with calculated sum spectra of individual carbons. We analyzed specifically the origin of the high-energy shoulder to the first pi*-resonance and identified contributions from the lowest-energy transition of a specific carbon in the phenyl and from transitions to higher unoccupied orbitals of the unmodified carbons in the C-60-cage. 

Place, publisher, year, edition, pages
2013. Vol. 568, 130-134 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-201237DOI: 10.1016/j.cplett.2013.03.031ISI: 000318320300025OAI: oai:DiVA.org:uu-201237DiVA: diva2:626881
Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The Electronic Structure of Organic Molecular Materials: Theoretical and Spectroscopic Investigations
Open this publication in new window or tab >>The Electronic Structure of Organic Molecular Materials: Theoretical and Spectroscopic Investigations
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively.

The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure is the first step in elucidating the photodegradation process. The electronic excitations from core levels to unoccupied molecular orbitals reveal not only the empty level structure of the molecule, but provide additional information related to the chemical bonds involving a specific atom type. In this way, they represent a means of determining the chemical changes that the molecule might withstand. The electronic transitions from carbon 1s core levels to unoccupied states are explained for the unmodified PCBM by a joint theoretical (DFT) and experimental study using the near edge x-ray absorption fine structure (NEXAFS) spectroscopy.

The second investigated system is the transition metal phthalocyanine with a manganese atom as the metal center. Manganese phthalocyanine (MnPc) is a single molecular magnet in which the spin switch process can be triggered by various methods. It has been shown, for instance, that the adsorption of hydrogen to the Mn center changes the spin state of the molecule from 3/2 to 1. More interestingly, the process is reversible and can be controlled, opening up the possibility of using MnPc as a quantum bit in magnetic memory devices. Up to this date, the d orbital occupation in MnPc has been under a long debate, both theoretical and experimental studies revealing different configurations. In this thesis the electronic structure of the phthalocyanine is thoroughly analysed by means of DFT and the calculated results are compared to photoelectron spectroscopy measurements. The combination of theoretical and experimental tools reveals that in gas phase at high temepratures the molecule exhibits a mixed electronic configuration. In this light, the possible control of the specific electronic state of the central metal represents an interesting prospect for molecular spintronics.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, Department of Physics and Astronomy, 2014. 76 p.
Keyword
materials theory, electronic structure, photoelectron spectroscopy, near-edge X-ray absorption fine structure
National Category
Atom and Molecular Physics and Optics Materials Chemistry Theoretical Chemistry Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics; Materials Science
Identifiers
urn:nbn:se:uu:diva-218225 (URN)
Presentation
2014-02-07, 2005, Uppsala, 14:00 (English)
Opponent
Supervisors
Available from: 2014-02-18 Created: 2014-02-10 Last updated: 2014-07-24Bibliographically approved
2. Molecules and Light: A Journey into the World of Theoretical Spectroscopy
Open this publication in new window or tab >>Molecules and Light: A Journey into the World of Theoretical Spectroscopy
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two of the main technological challenges of the century are the production of clean energy, on the one hand, and the development of new materials for electronic and spintronic applications that could increase the speed and the storage capacity of regular electronic devices, on the other hand. Organic materials, including fullerenes, organic polymers and organic molecules with metal centres are promising candidates for low-cost, flexible and clean technologies that can address these challenges. A thorough description of the electronic properties of such materials is, therefore, crucial. The interaction of electromagnetic radiation with the molecule can provide the needed insight into the electronic and vibrational levels and on possible chemical interactions. In order to explain and interpret experimentally measured spectra, a good theoretical description of the particular spectroscopy is necessary. Within density functional theory (DFT), the current thesis discusses the theoretical tools used to describe the spectroscopic properties of molecules with emphasis on two classes of organic materials for photovoltaics, molecular electronics and spintronics. Specifically, the stability of the fullerene derivative PC60BM is investigated in connection with its use as an electron acceptor in organic solar cells and the valence band electronic structure of several transition metal phthalocyanines is studied for their possible application in electronics and spintronics. The spectroscopies discussed in the current work are: the photoelectron spectroscopy of the valence band, X-ray photoelectron spectroscopy of the core levels, near-edge X-ray absorption fine structure, Infrared and Raman vibrational spectroscopies

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 109 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1393
Keyword
Theoretical spectroscopy, XPS, NEXAFS, PCBM, Metal phthalocyanine, Organic solar cells
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-300123 (URN)978-91-554-9630-2 (ISBN)
Public defence
2016-09-16, Polhemsalen, Ångström, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-08-26 Created: 2016-08-02 Last updated: 2016-09-20

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Brumboiu, Iulia E.Brena, Barbara

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