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  • 1. Man, Gabriel J.
    et al.
    Sterling, Cody M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamal, Chinnathambi
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Raja Ramanna Centre for Advanced Technology, India.
    Simonov, Konstantin A.
    Svanström, Sebastian
    Acharya, Joydev
    Johansson, Fredrik O. L.
    Giangrisostomi, Erika
    Ovsyannikov, Ruslan
    Huthwelker, Thomas
    Butorin, Sergei M.
    Nayak, Pabitra K.
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rensmo, Håkan
    Electronic coupling between the unoccupied states of the organic and inorganic sublattices of methylammonium lead iodide: A hybrid organic-inorganic perovskite single crystal2021Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, nr 4, artikkel-id L041302Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    Sterling, Cody
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Theoretical spectroscopic investigation of hybrid halide perovskite solar cell materials2020Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Perovskite solar cells have recently become a very promising candidate in the search for an effective solar cell material. Over the past 10 years, their power conversion efficiency has increased to over 25% and there is a wide range of different potential chemical makeups 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. This thesis aims to investigate the effect of material composition and structure on the electronic structure of the system. Two largely separate investigations are presented: first a study on the differences between MAPI (CH3NH3PbI3) and MAPB (CH3NH3PbBr3) and how differences in local structure can affect the N 1s X-ray absorption spectrum. Various geometric parameters are found to affect the shape of the spectrum and these are explained via specific orbital changes. Second, charge transfer between the MA+ ion and the inorganic PbI3 lattice inside MAPI is investigated, and this is paired with an explanation of hybridization of states between MAPI and its Pb-less precursor MAI (CH3NH3I).

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    abstract
  • 3.
    Sterling, Cody M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Modeling hybrid halide perovskites for solar cell applications: Simulations of electronic structure and X-ray spectroscopy2022Doktoravhandling, med artikler (Annet vitenskapelig)
    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).

    Fulltekst (pdf)
    Modeling hybrid halide perovskites for solar cell applications
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    Omslagsframsida
  • 4.
    Sterling, Cody M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    García-Fernández, Alberto
    Erbing, Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Svanström, Sebastian
    Kamal, Chinnathambi
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rensmo, Håkan
    Cappel, Ute B.
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Chemical Bonding in the α and δ Phases of FAPbI3Manuskript (preprint) (Annet vitenskapelig)
  • 5.
    Sterling, Cody M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamal, Chinnathambi
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Raja Ramanna Centre for Advanced Technology, India; Homi Bhabha National Institute, India.
    García-Fernández, Alberto
    Man, Gabriel J.
    Svanström, Sebastian
    Nayak, Pabitra K.
    Butorin, Sergei M.
    Rensmo, Håkan
    Cappel, Ute B.
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Electronic Structure and Chemical Bonding in Methylammonium Lead Triiodide and Its Precursor Methylammonium Iodide2022Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, nr 47, s. 20143-20154Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 6.
    Sterling, Cody M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kamal, Chinnathambi
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Raja Ramanna Centre for Advanced Technology, India.
    Man, Gabriel J.
    Nayak, Pabitra K.
    Simonov, Konstantin A.
    Svanström, Sebastian
    García-Fernández, Alberto
    Huthwelker, Thomas
    Cappel, Ute B.
    Butorin, Sergei M.
    Rensmo, Håkan
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Sensitivity of Nitrogen K-Edge X-ray Absorption to Halide Substitution and Thermal Fluctuations in Methylammonium Lead-Halide Perovskites2021Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 125, nr 15, s. 8360-8368Artikkel i tidsskrift (Fagfellevurdert)
    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.

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