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Jana, S., Panda, S. K., Phuyal, D., Pal, B., Mukherjee, S., Dutta, A., . . . Sarma, D. D. (2019). Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3. Physical Review B, 99(7), Article ID 075106.
Open this publication in new window or tab >>Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-378537 (URN)10.1103/PhysRevB.99.075106 (DOI)000458168300001 ()
Funder
Swedish Research Council, 2016-4524Knut and Alice Wallenberg Foundation, 2012.0031Swedish Energy Agency, P43294-1EU, European Research Council, CorrelMat-617196Swedish Research Council, 2016-03278Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation , CTS-17:376eSSENCE - An eScience CollaborationStandUp
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-21Bibliographically approved
Phuyal, D., Mukherjee, S., Jana, S., Denoel, F., Kamalakar, M. V., Butorin, S. M., . . . Karis, O. (2019). Ferroelectric properties of BaTiO3 thin films co-doped with Mn and Nb. AIP Advances, 9(9), Article ID 095207.
Open this publication in new window or tab >>Ferroelectric properties of BaTiO3 thin films co-doped with Mn and Nb
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2019 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 9, no 9, article id 095207Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Institute of Physics, 2019
Keywords
ferroelectric, complex oxides
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-393045 (URN)10.1063/1.5118869 (DOI)
Funder
Swedish Research Council, 2018-04330
Available from: 2019-09-13 Created: 2019-09-13 Last updated: 2019-09-13Bibliographically approved
Maibach, J., Källquist, I., Andersson, M., Urpelainen, S., Edström, K., Rensmo, H., . . . Hahlin, M. (2019). Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy. Nature Communications, 10, Article ID 3080.
Open this publication in new window or tab >>Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy
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2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 3080Article in journal (Refereed) Published
Abstract [en]

Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-390789 (URN)10.1038/s41467-019-10803-y (DOI)000475295300002 ()31300638 (PubMedID)
Funder
Swedish Research Council, 2016-03545Swedish Research Council, 2012-4681Swedish Research Council, 2014-6019Swedish Research Council, 2018-06465Swedish Energy Agency, 40495-1StandUpCarl Tryggers foundation
Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-15Bibliographically approved
Zhang, X., Cappel, U. B., Jia, D., Zhou, Q., Du, J., Sloboda, T., . . . Johansson, E. (2019). Probing and Controlling Surface Passivation of PbS Quantum Dot Solid for Improved Performance of Infrared Absorbing Solar Cells. Chemistry of Materials, 31(11), 4081-4091
Open this publication in new window or tab >>Probing and Controlling Surface Passivation of PbS Quantum Dot Solid for Improved Performance of Infrared Absorbing Solar Cells
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2019 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 11, p. 4081-4091Article in journal (Refereed) Published
Abstract [en]

Surface properties of colloidal quantum dots (CQDs) are critical for the transportation and recombination of the photoinduced charge carrier in CQD solar cells, therefore dominating the photovoltaic performance. Herein, PbS CQD passivated using liquid-state ligand exchange (LSLX) and solid-state ligand exchange (SSLX) strategies are in detail investigated using photoelectron spectroscopy (PES), and solar cell devices are prepared to understand the link between the CQD surface properties and the solar cell function. PES using different energies in the soft and hard Xray regime is applied to study the surface and bulk properties of the CQDs, and the results show more effective surface passivation of the CQDs prepared with the LSLX strategy and less formation of lead-oxide. The CQD solar cells prepared with LSLX strategy show higher performance, and the photoelectric measurements suggest that the recombination of photoinduced charges is reduced for the solar cell prepared with the LSLX approach. Meanwhile, the fabricated solar cells exhibit good stability. This work provides important insights into how to fine-tune the CQD surface properties by improving the CQD passivation, and how this is linked to further improvements of the device photovoltaic performance.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Materials Chemistry Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-390215 (URN)10.1021/acs.chemmater.9b00742 (DOI)000471728200026 ()
Funder
Swedish Energy AgencySwedish Research Council FormasSwedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and MedicineStiftelsen Olle Engkvist ByggmästareÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Available from: 2019-08-08 Created: 2019-08-08 Last updated: 2019-08-08Bibliographically approved
Jain, S. M., Phuyal, D., Davies, M. L., Li, M., Philippe, B., De Castro, C., . . . Durrant, J. R. (2018). 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. Nano Energy, 49, 614-624
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
Chernysheva, E., Srour, W., Philippe, B., Baris, B., Chenot, S., Felix Duarte, R., . . . Lazzari, R. (2018). Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study. Physical Review B, 97(23), Article ID 235430.
Open this publication in new window or tab >>Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 23, article id 235430Article in journal (Refereed) Published
Abstract [en]

Band alignment at the interface between evaporated silver films and Zn- or O-terminated polar orientations of ZnO is explored by combining soft and hard x-ray photoemissions on native and hydrogenated surfaces. Ultraviolet photoemission spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy, and Schottky barrier during silver deposition. The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by hard x-ray photoemission spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of similar to 0.3 monolayer of donorlike hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However, no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(000 (1) over bar)-O [anionic on ZnO(0001)-Zn] at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V-bb,(ZnO-O) = -0.4 eV and V-bb,(ZnO-Zn) = -0.6 eV found for the bare surfaces is reinforced upon hydrogenation (V-bb,(ZnO-O+H) = -1.1 eV, V-bb,(ZnO-Zn+H) = -1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-358511 (URN)10.1103/PhysRevB.97.235430 (DOI)000435638500004 ()
Funder
EU, FP7, Seventh Framework Programme, 312284
Available from: 2018-09-03 Created: 2018-09-03 Last updated: 2018-09-03Bibliographically approved
Lindblad, R., Oscarsson, J., Fredin, K., Eriksson, S. K., Siegbahn, H., Johansson, E. M. J. & Rensmo, H. (2018). Controlling energy level positions in hole conducting molecular films by additives. Journal of Electron Spectroscopy and Related Phenomena, 224, 100-106
Open this publication in new window or tab >>Controlling energy level positions in hole conducting molecular films by additives
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2018 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, p. 100-106Article in journal (Refereed) Published
Abstract [en]

Hard X-ray photoelectron spectroscopy (HAXPES) has been used to study the bulk electronic structure of thin molecular films of the organic compounds 2,2',7,7'-tetrakis (N,N'-di-p-methoxyphenyl-amine)-9,9'-spiro-bifluorene (spiro-OMeTAD), 4-(diethylamino)-benzaldehyde-1,1-diphenyl-hydrazone (DEH) and poly(3-hexylthiophene) (P3HT). Molecular layers of these compounds are hole conducting, a property that for example has been used in different solar cell configurations. The function of such a device benefits from the inclusion of additives such as Li-TFSI, or dopants such as Co-complexes, into the molecular layer. Here we report on effects of adding Li-TFSI to DEH and P3HT as observed by photoelectron spectroscopy and we compare with results on the spiro-OMeTAD hole conductor. It can be concluded that the Li-salt causes a shift of the Fermi level in DEH and P3HT towards the HOMO resulting in a p-doping of the molecular material. Similar shifts of the Fermi level could also be observed when adding different Co(+III) complexes to the Spiro-OMeTAD hole conductor, indicating means for more controlled doping.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
HAXPES, Mesoscopic solar cells, Spiro-OMeTAD, P3HT
National Category
Atom and Molecular Physics and Optics Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-221447 (URN)10.1016/j.elspec.2017.03.009 (DOI)000428825400016 ()
Funder
Swedish Research Council, 2012-4721EU, FP7, Seventh Framework Programme, 226716Carl Tryggers foundation Swedish Foundation for Strategic Research Swedish Energy AgencyGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology
Available from: 2014-03-31 Created: 2014-03-31 Last updated: 2018-10-05Bibliographically approved
Abdi-Jalebi, M., Pazoki, M., Philippe, B., Dar, M. I., Alsari, M., Sadhanala, A., . . . Friend, R. H. (2018). Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations. ACS Nano, 12(7), 7301-7311
Open this publication in new window or tab >>Dedoping of Lead Halide Perovskites Incorporating Monovalent Cations
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2018 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 7, p. 7301-7311Article in journal (Refereed) Published
Abstract [en]

We report significant improvements in the optoelectronic properties of lead halide perovskites with the addition of monovalent ions with ionic radii close to Pb2+. We investigate the chemical distribution and electronic structure of solution processed CH3NH3PbI3 perovskite structures containing Na+, Cu+, and Ag+, which are lower valence metal ions than Pb2+ but have similar ionic radii. Synchrotron X-ray diffraction reveals a pronounced shift in the main perovskite peaks for the monovalent cation-based films, suggesting incorporation of these cations into the perovskite lattice as well as a preferential crystal growth in Ag+ containing perovskite structures. Furthermore, the synchrotron X-ray photoelectron measurements show a significant change in the valence band position for Cu- and Ag-doped films, although the perovskite bandgap remains the same, indicating a shift in the Fermi level position toward the middle of the bandgap. Such a shift infers that incorporation of these monovalent cations dedope the n-type perovskite films when formed without added cations. This dedoping effect leads to cleaner bandgaps as reflected by the lower energetic disorder in the monovalent cation-doped perovskite thin films as compared to pristine films. We also find that in contrast to Ag+ and Cu+, Na+ locates mainly at the grain boundaries and surfaces. Our theoretical calculations confirm the observed shifts in X-ray diffraction peaks and Fermi level as well as absence of intrabandgap states upon energetically favorable doping of perovskite lattice by the monovalent cations. We also model a significant change in the local structure, chemical bonding of metal-halide, and the electronic structure in the doped perovskites. In summary, our work highlights the local chemistry and influence of monovalent cation dopants on crystallization and the electronic structure in the doped perovskite thin films.

Keywords
monovalent cations, dedoped perovskite thin films, enhanced optoelectronic quality, substitutional doping, interstitial doping
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-364505 (URN)10.1021/acsnano.8b03586 (DOI)000440505000097 ()29953817 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy AgencySwedish Foundation for Strategic Research StandUpEU, Horizon 2020, 687008Swedish National Infrastructure for Computing (SNIC), snice 2017-01-15; snice 2016-10-23
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2019-02-19Bibliographically approved
Svanström, S., Jacobsson, J., Sloboda, T., Giangrisostomi, E., Ovsyannikov, R., Rensmo, H. & Cappel, U. (2018). Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites. Journal of Materials Chemistry A, 6(44), 22134-22144
Open this publication in new window or tab >>Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites
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2018 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 44, p. 22134-22144Article in journal (Refereed) Published
Abstract [en]

Lead halide perovskite solar cells with multi-cation/mixed halide materials now give power conversion efficiencies of more than 20%. The stability of these mixed materials has been significantly improved through the addition of Cs+ compared to the original methylammonium lead iodide. However, it remains one of the most significant challenges for commercialisation. In this study, we use photoelectron spectroscopy (PES) in combination with visible laser illumination to study the photo-stability of perovskite films with different compositions. These include Br : I ratios of 50 : 50 and 17 : 83 and compositions with and without Cs+. For the samples without Cs and the 50 : 50 samples, we found that the surface was enriched in Br and depleted in I during illumination and that some of the perovskite decomposed into Pb0, organic halide salts, and iodine. After illumination, both of these reactions were partially reversible. Furthermore, the surfaces of the films were enriched in organic halide salts indicating that the cations were not degraded into volatile products. With the addition of Cs+ to the samples, photo-induced changes were significantly suppressed for a 50 : 50 bromide to iodide ratio and completely suppressed for perovskites with a 17 : 83 ratio at light intensities exceeding 1 sun equivalent.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-368425 (URN)10.1039/C8TA05795H (DOI)000456724800044 ()
Funder
Swedish Research Council, 2014-6019ÅForsk (Ångpanneföreningen's Foundation for Research and Development)Swedish Foundation for Strategic Research , RMA15-0130Swedish Energy Agency, P43294-1StandUp
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2019-02-18Bibliographically approved
Cappel, U. B., Liu, P., Johansson, F., Philippe, B., Giangrisostomi, E., Ovsyannikov, R., . . . Rensmo, H. (2018). Electronic Structure Characterization of Cross-Linked Sulfur Polymers. ChemPhysChem, 19(9), 1041-1047
Open this publication in new window or tab >>Electronic Structure Characterization of Cross-Linked Sulfur Polymers
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2018 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 9, p. 1041-1047Article in journal (Refereed) Published
Abstract [en]

Cross-linked polymers of elemental sulfur are of potential interest for electronic applications as they enable facile thin-film processing of an abundant and inexpensive starting material. Here, we characterize the electronic structure of a cross-linked sulfur/diisopropenyl benzene (DIB) polymer by a combination of soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES). Two different approaches for enhancing the conductivity of the polymer are compared: the addition of selenium in the polymer synthesis and the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) during film preparation. For the former, we observe the incorporation of Se into the polymer structure resulting in a changed valence-band structure. For the latter, a Fermi level shift in agreement with p-type doping of the polymer is observed and also the formation of a surface layer consisting mostly of TFSI anions.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2018
Keywords
cross-linking, hole-transporting material, solar cells, sulfur polymers, X-ray photoelectron spectroscopy
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-356387 (URN)10.1002/cphc.201800043 (DOI)000431492600005 ()29451358 (PubMedID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research Swedish Energy AgencySwedish Research Council, 2014-6463StandUp
Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-07-25Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-5949-0997

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