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Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
KTH Royal Institute of Technology. (Department of Chemistry)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.ORCID iD: 0000-0001-6776-5460
KTH Royal Institute of Technology. (Department of Chemistry)
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2018 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 30, no 15, p. 4959-4967Article in journal (Refereed) Published
Abstract [en]

Layered two-dimensional (2D) hybrid organic-inorganic perovskites (HOP) are promising materials for light-harvesting applications because of their chemical stability, wide flexibility in composition and dimensionality, and increases in photovoltaic power conversion efficiencies. Three 2D lead iodide perovskites were studied through various X-ray spectroscopic techniques to derive detailed electronic structures and band energetics profiles at a titania interface. Core-level and valence band photoelectron spectra of HOP were analyzed to resolve the electronic structure changes due to the reduced dimensionality of inorganic layers. The results show orbital narrowing when comparing the HOP, the layered precursor PbI2, and the conventional 3D (CH3NH3)PbI3 such that different localizations of band edge states and narrow band states are unambiguously due to the decrease in dimensionality of the layered HOPs. Support from density functional theory calculations provide further details on the interaction and band gap variations of the electronic structure. We observed an interlayer distance dependent dispersion in the near band edge electronic states. The results show how tuning the interlayer distance between the inorganic layers affects the electronic properties and provides important design principles for control of the interlayer charge transport properties, such as the change in effective charge masses as a function of the organic cation length. The results of these findings can be used to tune layered materials for optimal functionality and new applications.

Place, publisher, year, edition, pages
2018. Vol. 30, no 15, p. 4959-4967
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-361922DOI: 10.1021/acs.chemmater.8b00909ISI: 000442186500014OAI: oai:DiVA.org:uu-361922DiVA, id: diva2:1251758
Funder
StandUpSwedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg Foundation
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2018-11-02Bibliographically approved
In thesis
1. An X-ray Spectroscopic Study of Perovskites Oxides and Halides for Emerging Devices
Open this publication in new window or tab >>An X-ray Spectroscopic Study of Perovskites Oxides and Halides for Emerging Devices
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the electronic structures on several perovskite oxide and halide materials with a focus on light harvesting applications. The systematic study of the electronic properties of the transition metal oxides and post-transition metal halides is a key point if one is to understand their properties. The element and site selective nature of several x-ray based spectroscopic techniques are given special emphasis in order to obtain a complete picture of the electronic properties of the compounds in question. Much of the experimental studies are accompanied by ab initio calculations that corroborate with our experimental results.

In the oxide portion of this work, a new class of metallic oxides based on doping of an antiferromagnetic LaFeO3 was synthesized and systematically studied with x-ray absorption, x-ray emission, and photoemission spectroscopies. The compound’s electronic structure is complex, having itinerant as well as localized components that give rise to a unique physical state where antiferromagnetism, metallicity and charge-disproportionation coexist. Our resonant photoemission results establish that the Fe states in both magnetically ordered oxides show insulting properties, while the Mo states provide an itinerant band crossing the Fermi level. An excitation energy-dependent RIXS investigation on LaFe1-xMoxO3 and the double perovskite Sr2FeMoO6 revealed a double peak structure located in proximity to the elastic peak that is identified to purely d-d excitations, attributed to the strongly correlated nature of these transition metal compounds.

The growth of high-quality thin film ferroelectric based on BaTiO3 grown epitaxially by means of pulsed laser deposition were investigated. We systematically reduce the band gap of the ferroelectric thin film while retaining its polarization at ambient conditions in spite of the aliovalent doping. The electronic structure is studied by several x-ray techniques that show how the ferroelectricity persists as well as the effective reduction of the band gap through hybridized states.

In the post-transition metal halides, the valence and conduction bands were mapped using x-ray absorption, emission, and photoemission spectroscopies. The spectroscopic results identify the constituent states that form the valence band as well as the band energy positions, which is an imperative parameter in optoelectronic devices. In addition, x-ray based spectroscopy was used to demonstrate the stereochemical activity of lone-pair states (5s2 and 6s2) for several different halide compounds and their influence on the chemical, structural, and electronic properties of the material. Nanostructured halide perovskites are also explored. The position of iodine p states and valence band states in reduced dimensional lead-based compounds were examined, as their states are found to be confined in one crystallographic direction in contrast to their three-dimensional counterpart. This information highlights the interesting material properties and their use in current third generation solar cell research.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 84
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1740
Keywords
perovskite oxides, halide perovskites, x-ray spectroscopy, electronic structure
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-364407 (URN)978-91-513-0493-9 (ISBN)
Public defence
2018-12-14, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Available from: 2018-11-21 Created: 2018-10-26 Last updated: 2018-11-30

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Phuyal, DibyaPazoki, MeysamPhilippe, BertrandKaris, OlofButorin, SergeiRensmo, HåkanEdvinsson, Tomas

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