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  • 1.
    Jain, Sagar M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Davies, Matthew L.
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Li, Meng
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales;Soochow Univ, Inst Funct Nano & Soft Mat, Suzhou 215000, Peoples R China.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    De Castro, Catherine
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Qiu, Zhen
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kim, Jinhyun
    Imperial Coll London, Dept Chem, Exhibit Rd, London SW7 2AZ, England;Imperial Coll London, Ctr Plast Elect, Exhibit Rd, London SW7 2AZ, England.
    Watson, Trystan
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Tsoi, Wing Chung
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Durrant, James R.
    Swansea Univ Bay Campus, Coll Engn, SPECIFIC, Fabian Way, Swansea SA1 8EN, W Glam, Wales;Imperial Coll London, Dept Chem, Exhibit Rd, London SW7 2AZ, England;Imperial Coll London, Ctr Plast Elect, Exhibit Rd, London SW7 2AZ, England.
    An effective approach of vapour assisted morphological tailoring for reducing metal defect sites in lead-free, (CH3NH3)(3)Bi2I9 bismuth-based perovskite solar cells for improved performance and long-term stability2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 49, p. 614-624Article in journal (Refereed)
    Abstract [en]

    We present a controlled, stepwise formation of methylammonium bismuth iodide (CH3NH3)(3)Bi2I9 perovskite films prepared via the vapour assisted solution process (VASP) by exposing BiI3 films to CH3NH3I (MAI) vapours for different reaction times, (CH3NH3)(3)Bi2I9 semiconductor films with tunable optoelectronic properties are obtained. Solar cells prepared on mesoporous TiO2 substrates yielded hysteresis-free efficiencies upto 3.17% with good reproducibility. The good performance is attributed mainly to the homogeneous surface coverage, improved stoichiometry, reduced metallic content in the bulk, and desired optoelectronic properties of the absorbing material. In addition, solar cells prepared using pure BiI3 films without MAI exposure achieved a power conversion efficiency of 0.34%. The non-encapsulated (CH3NH3)(3)Bi2I9 devices were found to be stable for as long as 60 days with only 0.1% drop in efficiency. This controlled formation of (CH3NH3)(3)Bi2I9 perovskite films highlights the benefit of the VASP technique to optimize material stoichiometry, morphology, solar cell performance, and long-term durability.

  • 2.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India;Helmholtz Zentrum Berlin FG ISRR, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Panda, S. K.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Bennett Univ, Dept Phys, Greater Noida 201310, Uttar Pradesh, India.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, B.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Dutta, A.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Anil Kumar, Puri
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    IIT, CSRRI, Chicago, IL 60616 USA;IIT, Dept Phys, Chicago, IL 60616 USA.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, S.
    Univ Paris Saclay, Ctr Phys Theor, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France;Coll France, 11 Pl Marcelin Berthelot, F-75005 Paris, France.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sarma, D. D.
    Indian Inst Sci, Solid State & Struct Chem Unit, Bengaluru 560012, India.
    Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed)
    Abstract [en]

    We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

  • 3.
    Jana, Somnath
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Panda, Swarup
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Pal, Banabir
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Dutta, Anirban
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Hedlund, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Segre, Carlo U.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Biermann, Silke
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sarma, D.D.
    Doping induced site-selective Mott insulating phase in LaFeO3Manuscript (preprint) (Other academic)
    Abstract [en]

    Tailoring transport properties of strongly correlated electron systems in a controlled fashion counts among the dreams of materials scientists. In copper oxides, vary- ing the carrier concentration is a tool to obtain high- temperature superconducting phases. In manganites, dop- ing results in exotic physics such as insulator-metal tran- sitions (IMT), colossal magnetoresistance (CMR), orbital- or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides, antiferromagnetic order and CD phase is asssociated with insulating behavior. Here we re- port the realization of a unique physical state that can be induced by Mo doping in LaFeO3: the resulting metallic state is a site-selective Mott insulator where itinerant elec- trons evolving on low-energy Mo states coexist with local- ized carriers on the Fe sites. In addition, a local breathing- type lattice distortion induces charge disproportionation on the latter, without destroying the antiferromagnetic order. A state, combining antiferromangetism, metallic- ity and CD phenomena is rather rare in oxides and have utmost significance for future antiferromagnetic memory devices.

  • 4.
    Johansson, Malin B
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cameau, Mathis
    Zhu, Huimin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. 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, Theoretical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Cesium bismuth iodide, CsxBiyIz, solar cell compounds from systematic molar ratio variationManuscript (preprint) (Other academic)
  • 5.
    Paul, Souvik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Iusan, Diana
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Thunström, Patrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hellsvik, Johan
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, Electrum 229, SE-16440 Kista, Sweden..
    Pereiro, Manuel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, SeRC, SE-10044 Stockholm, Sweden..
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125120Article in journal (Refereed)
    Abstract [en]

    Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA+U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3d states, whereas the LDA+U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

  • 6.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    An X-ray Spectroscopic Study of Perovskites Oxides and Halides for Emerging Devices2018Doctoral 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.

    List of papers
    1. Electronic structure of the charge disproportionate and metallicity in LaFe1-xMoxO3 studied by resonant x-ray spectroscopies
    Open this publication in new window or tab >>Electronic structure of the charge disproportionate and metallicity in LaFe1-xMoxO3 studied by resonant x-ray spectroscopies
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    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    A metal-insulator transition and its intriguing properties were recently reported based on doping of the antiferromagnetic insulator LaFeO3. Through doping at the B site by Mo to the insulating perovskite LaFeO3 exhibits a coexistence of an antiferromagnetic ordering with room-temperature metallicity at higher doping levels, an unusual ground state for an oxide perovskite. Replacing Fe by Mo in the Fe-O6 octahedra enhances the separation of the two 2 Fe-O bonds relative to the orthorhombic LaFeO3, largely retaining the centrosymmetric character of the Fe sites, as confirmed through extended x-ray absorption fine structure. Mo ions appear to be homogeneously doped, with average valency of both metal sites monotonically decreasing with increasing Mo concentration. Resonant photoemission was recorded for both Fe and Mo to obtain element specific spectral information on the projected 3d and 4d partial density of states. The data shows gradual increase of spectral weight at the Fermi level that is attributed to Mo d states, while the Fe d states primarily reside at higher binding energy in the valence band, with significant hybridization with O 2p states. The RIXS spectra show strong electron correlation effects from d-d inelastic features and broad charge-transfer excitations for x = 0.2 where the compound becomes metallic. This is in contrast to the insulating parent LaFeO3 compound and insulating samples with lower Mo content. The coexistence of both bound and continuum excitations observed in the RIXS spectra provides strong evidence for charge disproportionation with features that are linked to the disproportionate Fe sites.

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-364367 (URN)
    Funder
    Knut and Alice Wallenberg Foundation, 2012.0031Swedish Energy Agency, P45349-1Swedish Research Council, 2014-6019Carl Tryggers foundation , CTS-17:376
    Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-10-26
    2. Valence electronic structure of the double perovskite Sr2FeMoO6 through resonant x-ray spectroscopies
    Open this publication in new window or tab >>Valence electronic structure of the double perovskite Sr2FeMoO6 through resonant x-ray spectroscopies
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Resonant x-ray spectroscopies were used to investigate the double perovskite Sr2FeMoO6 (SFMO) in order to identify the compounds valence electronic structure known for its half-metallicity and ferrimagnetism above room temperature. A comprehensive resonant photoelectron spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS) study was carried out to acquire a more detailed understanding and interpretation of the valence band electronic structure and hybridization between Fe and Mo d bands. The RPES spectrum clearly show enhancement of Mo d states at the Fermi level that are partly responsible for the metallic behavior. The RPES data at the Fe L3 edge shows strong hybridization with O 2p states as well hybridization with Mo d states. At the same time, characteristic d-d excitations are observed in the RIXS spectra at the Fe L edge indicative of Fe d states of more localized character. Although there are many valid definitions to the valency of the Fe and Mo ions and magnetic moments, the total electronic structure represented through element-resolved x-ray spectroscopies studies distinctly identifies the electronic states that results in its established correlated behavior and half-metallicity.

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-364368 (URN)
    Funder
    Carl Tryggers foundation , CTS-17:376Swedish Energy Agency, P43549-1Swedish Research Council, 2016-4524Knut and Alice Wallenberg Foundation, 2012.0031Swedish Foundation for Strategic Research , 15-0130
    Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-10-26
    3. The origin of low bandgap and ferroelectricity of a co-doped BaTiO3
    Open this publication in new window or tab >>The origin of low bandgap and ferroelectricity of a co-doped BaTiO3
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    2018 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 124, no 2, article id 27005Article in journal (Refereed) Published
    Abstract [en]

    We recently demonstrated the lowest bandgap bulk ferroelectric material, BaTi1-x(Mn1/2Nb1/2)xO3, a promising candidate material for visible light absorption in opto- electronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates with our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K-edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-364369 (URN)10.1209/0295-5075/124/27005 (DOI)000450630500002 ()
    Funder
    Swedish Foundation for Strategic Research , 15-0130Knut and Alice Wallenberg Foundation, 2012.0031Swedish Energy Agency, P43549-1Swedish Energy Agency, P43294-1Swedish Research Council, 2014-7019Swedish Research Council, 2016-4524
    Note

    Corection in: EPL, Volume: 124, Issue: 6, Article Number: 69901, DOI: 10.1209/0295-5075/124/69901

    Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2019-02-04Bibliographically approved
    4. Ferroelectric properties of doped BaTiO3 thin film by pulsed laser deposition
    Open this publication in new window or tab >>Ferroelectric properties of doped BaTiO3 thin film by pulsed laser deposition
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    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    BaTiO3 thin films co-doped at the Ti site with Mn and Nb were grown on 0.5% Nb-doped (001) oriented SrTiO3 substrates by pulsed laser deposition. The films show single-phase tetragonal structure, growing epitaxially with a smooth interface to the substrate. Using piezoforce microscopy, we find that both doped and undoped films exhibit good ferroelectric response. The piezoelectric domain switching in the films was confirmed by measuring local hysteresis of the polarization at several different areas across the thin films, demonstrating a switchable ferroelectric state for these films. The doping of the BaTiO3 also reduces the bandgap of the material from 3.18 eV for BaTiO3 to nearly 2.7 eV for the 7.5% doped sample, potentially making the films effective light-harvesters in the visible spectrum. The results demonstrate co-doping as an effective strategy for bandgap engineering and a guide for the realization of visible-light applications of related thin film systems.

    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-364370 (URN)
    Funder
    Swedish Research Council, 2014-6019Swedish Research Council, 2016-4524Swedish Energy Agency, P43549-1Knut and Alice Wallenberg Foundation, 2012.0031Swedish Foundation for Strategic Research , 15-0130
    Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-10-26
    5. Impact of synthetic routes on the structural and physical properties of butyl-1,4-diammonium lead iodide semiconductors
    Open this publication in new window or tab >>Impact of synthetic routes on the structural and physical properties of butyl-1,4-diammonium lead iodide semiconductors
    Show others...
    2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 23, p. 11730-11738Article in journal (Refereed) Published
    Abstract [en]

    We report the significant role of synthetic routes and the importance of solvents in the synthesis of organic-inorganic lead iodide materials. Through one route, the intercalation of dimethylformamide in the crystal structure was observed leading to a one-dimensional (1D) [NH3(CH2)(4)NH3]Pb2I6 structure of the product. This product was compared with the two-dimensional (2D) [NH3(CH2)(4)NH3]PbI4 recovered from aqueous solvent based synthesis with the same precursors. UV-visible absorption spectroscopy showed a red-shift of 0.1 eV for the band gap of the 1D network in relation to the 2D system. This shift primarily originates from a shift in the valence band edge as determined from photoelectron-and X-ray spectroscopy results. These findings also suggest the iodide 5p orbital as the principal component in the density of states in the valence band edge. Single crystal data show a change in the local coordination around iodide, while in both materials, lead atoms are surrounded by iodide atoms in octahedral units. The conductivity of the one-dimensional material ([NH3(CH2)(4)NH3]Pb2I6) was 50% of the two-d(i)mensional material ([NH3(CH2)(4)NH3]PbI4). The fabricated solar cells reflect these changes in the chemical and electronic structure of both materials, although the total light conversion efficiencies of solar cells based on both products were similar.

    Place, publisher, year, edition, pages
    ROYAL SOC CHEMISTRY, 2017
    National Category
    Materials Chemistry
    Identifiers
    urn:nbn:se:uu:diva-329653 (URN)10.1039/c6ta10123b (DOI)000403228200030 ()
    Funder
    StandUpSwedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg Foundation
    Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2018-10-26Bibliographically approved
    6. Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study
    Open this publication in new window or tab >>Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study
    Show others...
    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.

    National Category
    Condensed Matter Physics Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-361922 (URN)10.1021/acs.chemmater.8b00909 (DOI)000442186500014 ()
    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
    7. The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
    Open this publication in new window or tab >>The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
    Show others...
    2018 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 20, p. 9498-9505Article in journal (Refereed) Published
    Abstract [en]

    Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s(2)) states. The crystal structure of the two layered quasi-perovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices.

    National Category
    Materials Chemistry Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-357561 (URN)10.1039/c8ta00947c (DOI)000433427300020 ()
    Funder
    Swedish Research Council, 2014-6019Swedish Research Council, 2016-4524Swedish Energy Agency, P43549-1Swedish Foundation for Strategic Research , 15-0130Wallenberg Foundations, 2012.0031StandUp
    Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2019-02-19Bibliographically approved
    8. An effective approach of vapour assisted morphological tailoring for reducing metal defect sites in lead-free, (CH3NH3)(3)Bi2I9 bismuth-based perovskite solar cells for improved performance and long-term stability
    Open this publication in new window or tab >>An effective approach of vapour assisted morphological tailoring for reducing metal defect sites in lead-free, (CH3NH3)(3)Bi2I9 bismuth-based perovskite solar cells for improved performance and long-term stability
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    2018 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 49, p. 614-624Article in journal (Refereed) Published
    Abstract [en]

    We present a controlled, stepwise formation of methylammonium bismuth iodide (CH3NH3)(3)Bi2I9 perovskite films prepared via the vapour assisted solution process (VASP) by exposing BiI3 films to CH3NH3I (MAI) vapours for different reaction times, (CH3NH3)(3)Bi2I9 semiconductor films with tunable optoelectronic properties are obtained. Solar cells prepared on mesoporous TiO2 substrates yielded hysteresis-free efficiencies upto 3.17% with good reproducibility. The good performance is attributed mainly to the homogeneous surface coverage, improved stoichiometry, reduced metallic content in the bulk, and desired optoelectronic properties of the absorbing material. In addition, solar cells prepared using pure BiI3 films without MAI exposure achieved a power conversion efficiency of 0.34%. The non-encapsulated (CH3NH3)(3)Bi2I9 devices were found to be stable for as long as 60 days with only 0.1% drop in efficiency. This controlled formation of (CH3NH3)(3)Bi2I9 perovskite films highlights the benefit of the VASP technique to optimize material stoichiometry, morphology, solar cell performance, and long-term durability.

    Place, publisher, year, edition, pages
    ELSEVIER SCIENCE BV, 2018
    Keywords
    Vapour assisted solution process (VASP), Lead free perovskite, (CH3NH3)(3)Bi2I9, Morphological tailoring, High resolution X-ray photoelectron (HAXPES) spectroscopy
    National Category
    Materials Chemistry Condensed Matter Physics Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-358277 (URN)10.1016/j.nanoen.2018.05.003 (DOI)000434829500071 ()
    Funder
    Swedish Research CouncilEU, Horizon 2020, 663830
    Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2018-10-26Bibliographically approved
    9. Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells
    Open this publication in new window or tab >>Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells
    Show others...
    2018 (English)In: Advanced Energy Materials, ISSN 1614-6832, Vol. 8, no 6, article id 1702049Article in journal (Refereed) Published
    Abstract [en]

    Solution-processed colloidal quantum dot (CQD) solar cells harvesting the infrared part of the solar spectrum are especially interesting for future use in semitransparent windows or multilayer solar cells. To improve the device power conversion efficiency (PCE) and stability of the solar cells, surface passivation of the quantum dots is vital in the research of CQD solar cells. Herein, inorganic CsPbI3 perovskite (CsPbI3-P) coating on PbS CQDs with a low-temperature, solution-processed approach is reported. The PbS CQD solar cell with CsPbI3-P coating gives a high PCE of 10.5% and exhibits remarkable stability both under long-term constant illumination and storage under ambient conditions. Detailed characterization and analysis reveal improved passivation of the PbS CQDs with the CsPbI3-P coating, and the results suggest that the lattice coherence between CsPbI3-P and PbS results in epitaxial induced growth of the CsPbI3-P coating. The improved passivation significantly diminishes the sub-bandgap trap-state assisted recombination, leading to improved charge collection and therefore higher photovoltaic performance. This work therefore provides important insight to improve the CQD passivation by coating with an inorganic perovskite ligand for photovoltaics or other optoelectronic applications.

    Place, publisher, year, edition, pages
    WILEY-V C H VERLAG GMBH, 2018
    Keywords
    charge recombination, inorganic perovskite, quantum dots, solar cells, surface passivation
    National Category
    Physical Chemistry Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-348982 (URN)10.1002/aenm.201702049 (DOI)000426152400017 ()
    Funder
    Swedish Energy AgencySwedish Research CouncilSwedish Research Council Formas
    Available from: 2018-04-26 Created: 2018-04-26 Last updated: 2018-10-26Bibliographically approved
    10. Doping induced site-selective Mott insulating phase in LaFeO3
    Open this publication in new window or tab >>Doping induced site-selective Mott insulating phase in LaFeO3
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Tailoring transport properties of strongly correlated electron systems in a controlled fashion counts among the dreams of materials scientists. In copper oxides, vary- ing the carrier concentration is a tool to obtain high- temperature superconducting phases. In manganites, dop- ing results in exotic physics such as insulator-metal tran- sitions (IMT), colossal magnetoresistance (CMR), orbital- or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides, antiferromagnetic order and CD phase is asssociated with insulating behavior. Here we re- port the realization of a unique physical state that can be induced by Mo doping in LaFeO3: the resulting metallic state is a site-selective Mott insulator where itinerant elec- trons evolving on low-energy Mo states coexist with local- ized carriers on the Fe sites. In addition, a local breathing- type lattice distortion induces charge disproportionation on the latter, without destroying the antiferromagnetic order. A state, combining antiferromangetism, metallic- ity and CD phenomena is rather rare in oxides and have utmost significance for future antiferromagnetic memory devices.

    National Category
    Condensed Matter Physics
    Research subject
    Physics with spec. in Atomic, Molecular and Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-364365 (URN)
    Funder
    Swedish Research Council, 2014-6019Swedish Energy Agency, P43549-1Knut and Alice Wallenberg Foundation, 2012.0031
    Available from: 2018-10-25 Created: 2018-10-25 Last updated: 2018-11-01
  • 7.
    Phuyal, Dibya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Jain, Sagar Motilal
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Swansea Univ, Coll Engn, SPECIFIC, Bay Campus,Fabian Way, Swansea SA1 8EN, W Glam, Wales.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Johansson, Malin B
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Pazoki, Meysam
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kullgren, Jolla
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Kvashnina, Kristina O.
    ESRF, Rossendorf Beamline, CS40220, F-38043 Grenoble 9, France;HZDR, Inst Resource Ecol, POB 510119, D-01314 Dresden, Germany.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 20, p. 9498-9505Article in journal (Refereed)
    Abstract [en]

    Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s(2)) states. The crystal structure of the two layered quasi-perovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices.

  • 8.
    Phuyal, Dibya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Das, Shyamashis
    Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kvashnina, Kristina O.
    Rossendorf Beamline at ESRF - The European Synchrotron - CS40220, 38043 Grenoble Cedex 9, France; Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology - PO Box 510119, 01314 Dresden, Germany.
    Sarma, D.D.
    Department of Solid State and Structural Chemistry Unit, Indian Institute of Science - Bengaluru 560012, India.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    The origin of low bandgap and ferroelectricity of a co-doped BaTiO32018In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 124, no 2, article id 27005Article in journal (Refereed)
    Abstract [en]

    We recently demonstrated the lowest bandgap bulk ferroelectric material, BaTi1-x(Mn1/2Nb1/2)xO3, a promising candidate material for visible light absorption in opto- electronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound’s electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates with our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K-edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.

  • 9.
    Phuyal, Dibya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Mukherjee, Soham
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Jana, Somnath
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Denoel, Fernand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Butorin, Sergei M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kalaboukhov, Alexei
    Department of Microtechnology and Nanoscience, Chalmers University of Technology, S-41296 Gothenburg, Sweden.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ferroelectric properties of BaTiO3 thin films co-doped with Mn and Nb2019In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 9, no 9, article id 095207Article in journal (Refereed)
    Abstract [en]

    We report on properties of BaTiO3 thin films where the bandgap is tuned via aliovalent doping of Mn and Nb ions co-doped at the Ti site. The doped films show single-phase tetragonal structure, growing epitaxially with a smooth interface to the substrate. Using piezoforce microscopy, we find that both doped and undoped films exhibit good ferroelectric response. The piezoelectric domain switching in the films was confirmed by measuring local hysteresis of the polarization at several different areas across the thin films, demonstrating a switchable ferroelectric state. The doping of the BaTiO3 also reduces the bandgap of the material from 3.2 eV for BaTiO3 to nearly 2.7 eV for the 7.5% doped sample, suggesting the viability of the films for effective light harvesting in the visible spectrum. The results demonstrate co-doping as an effective strategy for bandgap engineering and a guide for the realization of visible-light applications using its ferroelectric properties.

  • 10.
    Phuyal, Dibya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Safdari, Majid
    KTH Royal Institute of Technology.
    Pazoki, Meysam
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Liu, Peng
    KTH Royal Institute of Technology.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kvashnina, Kristina O.
    ESRF.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kloo, Lars
    KTH Royal Institute of Technology.
    Gardner, James
    KTH Royal Institute of Technology.
    Electronic Structure of Two-Dimensional Lead(II) Iodide Perovskites: An Experimental and Theoretical Study2018In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 30, no 15, p. 4959-4967Article in journal (Refereed)
    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.

  • 11.
    Safdari, Majid
    et al.
    KTH Royal Inst Technol, Dept Chem, Appl Phys Chem, SE-10044 Stockholm, Sweden..
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Svensson, Per H.
    KTH Royal Inst Technol, Dept Chem, Appl Phys Chem, SE-10044 Stockholm, Sweden.;SP Proc Dev, Sodertalje, Sweden..
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kvashnina, Kristina O.
    ESRF European Synchrotron, CS40220, F-38043 Grenoble 9, France.;Helmholtz Zentrum Dresden Rossendorf, Inst Resource Ecol, D-01314 Dresden, Germany..
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kloo, Lars
    KTH Royal Inst Technol, Dept Chem, Appl Phys Chem, SE-10044 Stockholm, Sweden..
    Gardner, James M.
    KTH Royal Inst Technol, Dept Chem, Appl Phys Chem, SE-10044 Stockholm, Sweden..
    Impact of synthetic routes on the structural and physical properties of butyl-1,4-diammonium lead iodide semiconductors2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 23, p. 11730-11738Article in journal (Refereed)
    Abstract [en]

    We report the significant role of synthetic routes and the importance of solvents in the synthesis of organic-inorganic lead iodide materials. Through one route, the intercalation of dimethylformamide in the crystal structure was observed leading to a one-dimensional (1D) [NH3(CH2)(4)NH3]Pb2I6 structure of the product. This product was compared with the two-dimensional (2D) [NH3(CH2)(4)NH3]PbI4 recovered from aqueous solvent based synthesis with the same precursors. UV-visible absorption spectroscopy showed a red-shift of 0.1 eV for the band gap of the 1D network in relation to the 2D system. This shift primarily originates from a shift in the valence band edge as determined from photoelectron-and X-ray spectroscopy results. These findings also suggest the iodide 5p orbital as the principal component in the density of states in the valence band edge. Single crystal data show a change in the local coordination around iodide, while in both materials, lead atoms are surrounded by iodide atoms in octahedral units. The conductivity of the one-dimensional material ([NH3(CH2)(4)NH3]Pb2I6) was 50% of the two-d(i)mensional material ([NH3(CH2)(4)NH3]PbI4). The fabricated solar cells reflect these changes in the chemical and electronic structure of both materials, although the total light conversion efficiencies of solar cells based on both products were similar.

  • 12.
    Serrano, I. G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Panda, Jaganandha
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Denoel, Fernand
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Vallin, Örjan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Two-Dimensional Flexible High Diffusive Spin Circuits2019In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, no 2, p. 666-673Article in journal (Refereed)
    Abstract [en]

    Owing to their unprecedented electronic properties, graphene and two-dimensional (2D) crystals have brought fresh opportunities for advances in planar spintronic devices. Graphene is an ideal medium for spin transport while being an exceptionally resilient material for flexible nanoelectronics. However, these extraordinary traits have never been combined to create flexible graphene spin circuits. Realizing such circuits could lead to bendable strain-spin sensors, as well as a unique platform to explore pure spin current based operations and low-power 2D flexible nanoelectronics. Here, we demonstrate graphene spin circuits on flexible substrates for the first time. Despite the rough topography of the flexible substrates, these circuits prepared with chemical vapor deposited monolayer graphene reveal an efficient room temperature spin transport with distinctively large spin diffusion coefficients ∼0.2 m2 s–1. Compared to earlier graphene devices on Si/SiO2 substrates, such values are up to 20 times larger, leading to one order higher spin signals and an enhanced spin diffusion length ∼10 μm in graphene-based nonlocal spin valves fabricated using industry standard systems. This high performance arising out of a characteristic substrate terrain shows promise of a scalable and flexible platform towards flexible 2D spintronics. Our innovation is a key step for the exploration of strain-dependent 2D spin phenomena and paves the way for flexible graphene spin memory–logic units and planar spin sensors.

  • 13.
    Zhang, Xiaoliang
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Zhang, Jindan
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Phuyal, Dibya
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Du, Juan
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Tian, Lei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Öberg, Viktor A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Johansson, Malin B
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Cappel, Ute B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala Univ, Mol & Condensed Matter Phys, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Liu, Jianhua
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Boschloo, Gerrit
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Johansson, Erik M. J.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells2018In: Advanced Energy Materials, ISSN 1614-6832, Vol. 8, no 6, article id 1702049Article in journal (Refereed)
    Abstract [en]

    Solution-processed colloidal quantum dot (CQD) solar cells harvesting the infrared part of the solar spectrum are especially interesting for future use in semitransparent windows or multilayer solar cells. To improve the device power conversion efficiency (PCE) and stability of the solar cells, surface passivation of the quantum dots is vital in the research of CQD solar cells. Herein, inorganic CsPbI3 perovskite (CsPbI3-P) coating on PbS CQDs with a low-temperature, solution-processed approach is reported. The PbS CQD solar cell with CsPbI3-P coating gives a high PCE of 10.5% and exhibits remarkable stability both under long-term constant illumination and storage under ambient conditions. Detailed characterization and analysis reveal improved passivation of the PbS CQDs with the CsPbI3-P coating, and the results suggest that the lattice coherence between CsPbI3-P and PbS results in epitaxial induced growth of the CsPbI3-P coating. The improved passivation significantly diminishes the sub-bandgap trap-state assisted recombination, leading to improved charge collection and therefore higher photovoltaic performance. This work therefore provides important insight to improve the CQD passivation by coating with an inorganic perovskite ligand for photovoltaics or other optoelectronic applications.

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