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Modeling hybrid halide perovskites for solar cell applications: Simulations of electronic structure and X-ray spectroscopy
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0001-9518-9405
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the past 13 years, perovskites have become a very promising candidate in the search for cheap and effective photovoltaic materials for solar cells.  Perovskite solar cell power conversion efficiency has increased from 3.8% in 2009 to over 25% by late 2022, rivaling that of crystalline silicon cells, and there are a variety of potential chemical compositions that provide a range of materials to investigate.  However, there are still questions about the specific role of all the different chemical components in the material and how they influence its efficiency.  This thesis aims to investigate the effect of material composition and structure through electronic structure calculations and theoretical X-ray absorption and X-ray photoelectron spectroscopy, with comparison to experimental spectra.  Herein, studies on the prototypical hybrid halide perovskite methylammonium lead triiodide (CH3NH3PbI3) are presented and compared among materials with various differences: structural/elemental changes in the case of its precursor methylammonium iodide (CH3NH3I), halide substitution in the case of methylammonium lead tribromide (CH3NH3PbBr3), or organic cation substitution in the case of formamidinium lead triiodide (CH(NH2)2PbI3).

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2022. , p. 54
Keywords [en]
Solar cells, perovskites, computational chemistry, simulations, electronic structure, density functional theory, X-ray spectroscopy
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-211949ISBN: 978-91-8014-114-7 (print)ISBN: 978-91-8014-115-4 (electronic)OAI: oai:DiVA.org:su-211949DiVA, id: diva2:1714497
Public defence
2023-01-13, Lärosal 14, Albano Hus 2, Albanovägen 18, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 2017-006797Available from: 2022-12-20 Created: 2022-11-29 Last updated: 2022-12-12Bibliographically approved
List of papers
1. Electronic Structure and Chemical Bonding in Methylammonium Lead Triiodide and Its Precursor Methylammonium Iodide
Open this publication in new window or tab >>Electronic Structure and Chemical Bonding in Methylammonium Lead Triiodide and Its Precursor Methylammonium Iodide
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2022 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 47, p. 20143-20154Article in journal (Refereed) Published
Abstract [en]

A detailed examination of the electronic structures of methylammonium lead triiodide (MAPI) and methylammonium iodide (MAI) is performed with ab initio molecular dynamics (AIMD) simulations based on density functional theory, and the theoretical results are compared to experimental probes. The occupied valence bands of a MAPI single crystal and MAI powder are probed with X-ray photoelectron spectroscopy, and the conduction bands are probed from the perspective of nitrogen K-edge X-ray absorption spectroscopy. Combined, the theoretical simulations and the two experimental techniques allow for a dissection of the electronic structure unveiling the nature of chemical bonding in MAPI and MAI. Here, we show that the difference in band gap between MAPI and MAI is caused chiefly by interactions between iodine and lead but also weaker interactions with the MA+ counterions. Spatial decomposition of the iodine p levels allows for analysis of Pb–I σ bonds and π interactions, which contribute to this effect with the involvement of the Pb 6p levels. Differences in hydrogen bonding between the two materials, seen in the AIMD simulations, are reflected in nitrogen valence orbital composition and in nitrogen K-edge X-ray absorption spectra.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-211925 (URN)10.1021/acs.jpcc.2c06782 (DOI)000888147500001 ()2-s2.0-85142648869 (Scopus ID)
Funder
Swedish Research Council Formas, 2019-02496Swedish Research Council, 2018- 05973Swedish Research Council, 2018-04125Swedish Research Council, 2018-04330Swedish Research Council, 2018-05525Swedish Research Council, 2018-06465Swedish Research Council, 2018-07152Swedish Energy Agency, 2017-006797Swedish Energy Agency, STEM P50626-1Göran Gustafsson Foundation for Research in Natural Sciences and MedicineVinnova, 2018-04969
Available from: 2022-11-29 Created: 2022-11-29 Last updated: 2023-01-10Bibliographically approved
2. Electronic coupling between the unoccupied states of the organic and inorganic sublattices of methylammonium lead iodide: A hybrid organic-inorganic perovskite single crystal
Open this publication in new window or tab >>Electronic coupling between the unoccupied states of the organic and inorganic sublattices of methylammonium lead iodide: A hybrid organic-inorganic perovskite single crystal
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2021 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 4, article id L041302Article in journal (Refereed) Published
Abstract [en]

Organic-inorganic halide perovskites have been intensively reinvestigated due to their applications, yet the optoelectronic function of the organic cation remains unclear. Through organic-selective resonant Auger electron spectroscopy measurements on well-defined single-crystal surfaces, we find evidence for electronic coupling in the unoccupied states between the organic and inorganic sublattices of the prototypical hybrid perovskite, which is contrary to the notion based on previous studies that the organic cation is electronically inert. The coupling is relevant for electron dynamics in the material and for understanding optoelectronic functionality.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:su:diva-197075 (URN)10.1103/PhysRevB.104.L041302 (DOI)000678811100009 ()
Available from: 2021-09-23 Created: 2021-09-23 Last updated: 2022-11-29Bibliographically approved
3. Sensitivity of Nitrogen K-Edge X-ray Absorption to Halide Substitution and Thermal Fluctuations in Methylammonium Lead-Halide Perovskites
Open this publication in new window or tab >>Sensitivity of Nitrogen K-Edge X-ray Absorption to Halide Substitution and Thermal Fluctuations in Methylammonium Lead-Halide Perovskites
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2021 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, no 15, p. 8360-8368Article in journal (Refereed) Published
Abstract [en]

The performance of hybrid perovskite materials in solar cells crucially depends on their electronic properties, and it is important to investigate contributions to the total electronic structure from specific components in the material. In a combined theoretical and experimental study of CH3NH3PbI3-methylammonium lead triiodide (MAPI)-and its bromide cousin CH3NH3PbBr3 (MAPB), we analyze nitrogen K-edge (N Is-to-2p*) X-ray absorption (XA) spectra measured in MAPI and MAPB single crystals. This permits comparison of spectral features to the local character of unoccupied molecular orbitals on the CH3NH3+ (MA(+)) counterions and allows us to investigate how thermal fluctuations, hydrogen bonding, and halide-ion substitution influence the XA spectra as a measure of the local electronic structure. In agreement with the experiment, the simulated spectra for MAPI and MAPB show close similarity, except that the MAPB spectral features are blue-shifted by +0.31 eV. The shift is shown to arise from the intrinsic difference in the electronic structure of the two halide atoms rather than from structural differences between the materials. In addition, from the spectral sampling analysis of molecular dynamics simulations, clear correlations between geometric descriptors(N-C, N-H, and H center dot center dot center dot I/Br distances) and spectral features are identified and used to explain the spectral shapes.

Keywords
Crystal structure, Ions, Nitrogen, Noncovalent interactions, Mathematical methods
National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-194122 (URN)10.1021/acs.jpcc.1c02017 (DOI)000644438400036 ()
Available from: 2021-06-16 Created: 2021-06-16 Last updated: 2022-11-29Bibliographically approved
4. Experimental and Theoretical Core Level and Valence Band Analysis of Clean Perovskite Single Crystal Surfaces
Open this publication in new window or tab >>Experimental and Theoretical Core Level and Valence Band Analysis of Clean Perovskite Single Crystal Surfaces
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2022 (English)In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 18, no 13, article id 2106450Article in journal (Refereed) Published
Abstract [en]

A detailed understanding of the surface and interface properties of lead halide perovskites is of interest for several applications, in which these materials may be used. To develop this understanding, the study of clean crystalline surfaces can be an important stepping stone. In this work, the surface properties and electronic structure of two different perovskite single crystal compositions (MAPbI3 and CsxFA1–xPbI3) are investigated using synchrotron-based soft X-ray photoelectron spectroscopy (PES), molecular dynamics simulations, and density functional theory. The use of synchrotron-based soft X-ray PES enables high surface sensitivity and nondestructive depth-profiling. Core level and valence band spectra of the single crystals are presented. The authors find two carbon 1s contributions at the surface of MAPbI3 and assign these to MA+ ions in an MAI-terminated surface and to MA+ ions below the surface. It is estimated that the surface is predominantly MAI-terminated but up to 30% of the surface can be PbI2-terminated. The results presented here can serve as reference spectra for photoelectron spectroscopy investigations of technologically relevant polycrystalline thin films, and the findings can be utilized to further optimize the design of device interfaces.

Keywords
molecular dynamics, perovskite single crystals, soft X-ray photoelectron spectroscopy, synchrotron radiation, Z+1 calculation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-202287 (URN)10.1002/smll.202106450 (DOI)000751394300001 ()35122466 (PubMedID)2-s2.0-85124454289 (Scopus ID)
Available from: 2022-02-23 Created: 2022-02-23 Last updated: 2022-11-29Bibliographically approved
5. Chemical Bonding in the α and δ Phases of FAPbI3
Open this publication in new window or tab >>Chemical Bonding in the α and δ Phases of FAPbI3
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(English)Manuscript (preprint) (Other academic)
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-211924 (URN)
Available from: 2022-11-29 Created: 2022-11-29 Last updated: 2022-11-29

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