| 1. |
- Maibach, Julia, et al.
(författare)
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Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy
- 2019
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Yang, Lei, et al.
(författare)
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Experimental and Theoretical Investigation of the Function of 4- tert -Butyl Pyridine for Interface Energy Level Adjustment in Efficient Solid-State Dye-Sensitized Solar Cells
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society. - 1944-8244 .- 1944-8252. ; 10:14, s. 11572-11579
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Tidskriftsartikel (refereegranskat)abstract
- 4-tert-Butylpyridine (t-BP) is commonly used in solid state dye-sensitized solar cells (ssDSSCs) to increase the photovoltaic performance. In this report, the mechanism how t-BP functions as a favorable additive is investigated comprehensively. ssDSSCs were prepared with different concentrations of t-BP, and a clear increase in efficiency was observed up to a maximum concentration and for higher concentrations the efficiency thereafter decreases. The energy level alignment in the complete devices was measured using hard X-ray photoelectron spectroscopy (HAXPES). The results show that the energy levels of titanium dioxide are shifted further away from the energy levels of spiro-OMeTAD as the t-BP concentration is increased. This explains the higher photovoltage obtained in the devices with higher t-BP concentration. In addition, the electron lifetime was measured for the devices and the electron lifetime was increased when adding t-BP, which can be explained by the recombination blocking effect at the surface of TiO2. The results from the HAXPES measurements agree with those obtained from density functional theory calculations and give an understanding of the mechanism for the improvement, which is an important step for the future development of solar cells including t-BP.
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| 3. |
- Jacobsson, Jesper, 1984-, et al.
(författare)
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Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:25, s. 13548-13557
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Tidskriftsartikel (refereegranskat)abstract
- A trend in high performing lead halide perovskite solar cell devices has been increasing compositional complexity by successively introducing more elements, dopants, and additives into the structure; and some of the latest top efficiencies have been achieved with a quadruple cation mixed halide perovskite Cs(x)FA(y)MA(z)Rb(1-x-y-z)PbBr(q)I(3-9). This paper continues this trend by exploring doping of mixed lead halide perovskites, FA(0.83)MA(0.17)PbBr(0.51)I(2.49), with an extended set of alkali cations, i.e., Cs+, Rb+, K+, and Na+, as well as combinations of them. The doped perovskites were investigated with X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, hard X-ray photoelectron spectroscopy, UV-vis, steady state fluorescence, and ultrafast transient absorption spectroscopy. Solar cell devices were made as well. Cs+ can replace the organic cations in the perovskite structure, but Rb+, K+, and Na+ do not appear to do that. Despite this, samples doped with K and Na have substantially longer fluorescence lifetimes, which potentially could be beneficial for device performance.
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| 4. |
- Man, Gabriel J., et al.
(författare)
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A-site cation influence on the conduction band of lead bromide perovskites
- 2022
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Ingår i: Nature Communications. - : Nature Research. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Hot carrier solar cells hold promise for exceeding the Shockley-Queisser limit. Slow hot carrier cooling is one of the most intriguing properties of lead halide perovskites and distinguishes this class of materials from competing materials used in solar cells. Here we use the element selectivity of high-resolution X-ray spectroscopy and density functional theory to uncover a previously hidden feature in the conduction band states, the sigma-pi energy splitting, and find that it is strongly influenced by the strength of electronic coupling between the A-cation and bromide-lead sublattice. Our finding provides an alternative mechanism to the commonly discussed polaronic screening and hot phonon bottleneck carrier cooling mechanisms. Our work emphasizes the optoelectronic role of the A-cation, provides a comprehensive view of A-cation effects in the crystal and electronic structures, and outlines a broadly applicable spectroscopic approach for assessing the impact of chemical alterations of the A-cation on perovskite electronic structure. The A-cation influence on the mechanism of slow hot carrier cooling in perovskites is controversial. Here, Man et al. resolve a debated issue regarding A-cation influence on the electronic structure of lead halide perovskites.
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| 5. |
- Sterling, Cody M., et al.
(författare)
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Sensitivity of Nitrogen K-Edge X-ray Absorption to Halide Substitution and Thermal Fluctuations in Methylammonium Lead-Halide Perovskites
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:15, s. 8360-8368
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Tidskriftsartikel (refereegranskat)abstract
- The performance of hybrid perovskite materials in solar cells crucially depends on their electronic properties, and it is important to investigate contributions to the total electronic structure from specific components in the material. In a combined theoretical and experimental study of CH3NH3PbI3-methylammonium lead triiodide (MAPI)-and its bromide cousin CH3NH3PbBr3 (MAPB), we analyze nitrogen K-edge (N Is-to-2p*) X-ray absorption (XA) spectra measured in MAPI and MAPB single crystals. This permits comparison of spectral features to the local character of unoccupied molecular orbitals on the CH3NH3+ (MA(+)) counterions and allows us to investigate how thermal fluctuations, hydrogen bonding, and halide-ion substitution influence the XA spectra as a measure of the local electronic structure. In agreement with the experiment, the simulated spectra for MAPI and MAPB show close similarity, except that the MAPB spectral features are blue-shifted by +0.31 eV. The shift is shown to arise from the intrinsic difference in the electronic structure of the two halide atoms rather than from structural differences between the materials. In addition, from the spectral sampling analysis of molecular dynamics simulations, clear correlations between geometric descriptors(N-C, N-H, and H center dot center dot center dot I/Br distances) and spectral features are identified and used to explain the spectral shapes.
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| 6. |
- Lindblad, Rebecka, et al.
(författare)
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Controlling energy level positions in hole conducting molecular films by additives
- 2018
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 224, s. 100-106
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Phuyal, Dibya, 1985-, et al.
(författare)
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Nonlocal Interactions in the Double Perovskite Sr2FeMoO6 from Core-Level X‐ray Spectroscopy
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125, s. 11249-11256
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Tidskriftsartikel (refereegranskat)abstract
- The valence electronic structure of the half-metallicdouble perovskite Sr2FeMoO6 forms from a strongly hybridizedband in the spin-down channel of Fe 3d and Mo 4d states thatprovides metallic conductivity and a gapped spin-up channel. Theground-state description has previously been explored in terms ofmany-body interactions where local and nonlocal interactionsproduce states with a combination of a charge-transferconfiguration and intersite charge fluctuations. Here, we providea qualitative understanding on nonlocal effects in Sr2FeMoO6using a combination of core-level X-ray spectroscopies, specificallyX-ray absorption, emission, and photoelectron spectroscopies. Ourspectroscopic data indicate intersite Fe 4p−O 2p−Mo 4dinteractions to be the origin of these nonlocalized transitions.Close to the Fermi level, this interaction is dominated by Mo 4d−O 2p character. When our data are compared against first- principles electronic structure calculations, we conclude that a full understanding of the nature of these states requires a spin-resolved description of the hybridization functions and that the nonlocal screening occurs predominantly through hybridization in the minority spin channel of the Mo 4d bands.
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| 8. |
- Westermark, Karin, et al.
(författare)
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PES Studies of Ru(dcbpyH2)2(NCS)2 Adsorption on Nanostructured ZnO for Solar Cell Applications
- 2002
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 106:39, s. 10102-10107
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between the dye cis-bis(4,4‘-dicarboxy-2,2‘-bipyridine)-bis(isothiocyanato)-ruthenium(II), Ru(dcbpyH2)2(NCS)2, and nanostructured ZnO was investigated by photoelectron spectroscopy (PES) using synchrotron radiation. The results are compared with those of nanostructured TiO2 sensitized with the same dye, which to date is the most efficient system for dye-sensitized photoelectrochemical solar cells. When comparing the two metal oxides, differences in the surface molecular structure were observed both for low and high dye coverages, as seen by comparing the oxygen, nitrogen and sulfur signals. The origin of these differences is discussed in terms of substrate-induced dye aggregation and in variations in surface bonding geometries. The measurements also provide information concerning the energy matching between the orbitals of the dye and the ZnO valence band, which is of importance in photoinduced charge transfer.
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| 9. |
- Cappel, Ute B., et al.
(författare)
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Characterization of the Interface Properties and Processes in Solid State Dye-Sensitized Solar Cells Employing a Perylene Sensitizer
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:10, s. 4345-4358
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Tidskriftsartikel (refereegranskat)abstract
- We recently reported on a perylene sensitizer, ID176, which performs much better in solid state dye-sensitized solar cells than in those using liquid electrolytes with iodide/tri-iodide as the redox couple (J. Phys. Chem. C2009, 113, 14595-14597). Here, we present a characterization of the sensitizer and of the TiO2/dye interface by UV-visible absorption and fluorescence spectroscopy, spectroelectrochemistry, photoelectron spectroscopy, electroabsorption spectroscopy, photoinduced absorption spectroscopy, and femtosecond transient absorption measurements. We report that the absorption spectrum of the sensitizer is red-shifted by addition of lithium ions to the surface due to a downward shift of the excited state level of the sensitizer, which is of the same order of magnitude as the downward shift of the titanium dioxide conduction band edge. Results from photoelectron spectroscopy and electrochemistry suggest that the excited state is largely located below the conduction band edge of TiO2 but that there are states in the band gap of TiO2 which might be available for photoinduced electron injection. The sensitizer was able to efficiently inject into TiO2, when a lithium salt was present on the surface, while injection was much less effective in the absence of lithium ions or in the presence of solvent. In the presence of the hole conductor 2,2-,7,7-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9-spirobifluorene (spiro-MeOTAD) and LiTFSI, charge separation was monitored by the emergence of a Stark shift of the dye in transient absorption spectra, and both injection and regeneration appear to be completed within 1 ps. Regeneration by spiro-MeOTAD is therefore several orders of magnitude faster than regeneration by iodide, and ID176 can even be photoreduced by spiro-MeOTAD.
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| 10. |
- Daniel, Quentin, et al.
(författare)
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Re-Investigation of Cobalt Porphyrin for Electrochemical Water Oxidation on FTO Surface : Formation of CoOx as Active Species
- 2017
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:2, s. 1143-1149
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Tidskriftsartikel (refereegranskat)abstract
- The use of cobalt porphyrin complexes as efficient and cost-effective molecular catalysts for water oxidation has been investigated previously. However, by combining a set of analytical techniques (electrochemistry, ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and synchrotron-based photoelectron spectroscopy (SOXPES and HAXPES)), we have demonstrated that three different cobalt porphyrins, deposited on FTO glasses, decompose promptly into a thin film of CoOx on the surface of the electrode during water oxidation under certain conditions (borate buffer pH 9.2). It is presumed that the film is composed of CoO, only detectable by SOXPES, as conventional techniques are ineffective. This newly formed film has a high turnover frequency (TOF), while the high transparency of the CoOx-based electrode is very promising for future application in photoelectrochemical cells.
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