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- Cappel, Ute B, et al.
(författare)
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Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells.
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:40, s. 34970-34978
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Tidskriftsartikel (refereegranskat)abstract
- ) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.
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| 2. |
- Giangrisostomi, Erika, et al.
(författare)
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Low Dose Photoelectron Spectroscopy at BESSY II : Electronic structure of matter in its native state
- 2018
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 224:SI, s. 68-78
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Tidskriftsartikel (refereegranskat)abstract
- The implementation of a high-transmission, angular-resolved time-of-Right electron spectrometer with a 1.25 MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS2 are presented to demonstrate the instrument performances. (C) 2017 The Authors. Published by Elsevier B.V.
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| 3. |
- Wernet, Ph., et al.
(författare)
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Communication : Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm
- 2017
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 146:21
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Tidskriftsartikel (refereegranskat)abstract
- We prove the hitherto hypothesized sequential dissociation of Fe(CO)(5) in the gas phase upon photoexcitation at 266 nm via a singlet pathway with time-resolved valence and core-level photoelectron spectroscopy with an x-ray free-electron laser. Valence photoelectron spectra are used to identify free CO molecules and to determine the time constants of stepwise dissociation to Fe(CO)(4) within the temporal resolution of the experiment and further to Fe(CO)(3) within 3 ps. Fe 3p core-level photoelectron spectra directly reflect the singlet spin state of the Fe center in Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) showing that the dissociation exclusively occurs along a singlet pathway without triplet-state contribution. Our results are important for assessing intra- and intermolecular relaxation processes in the photodissociation dynamics of the prototypical Fe(CO)(5) complex in the gas phase and in solution, and they establish time-resolved core-level photoelectron spectroscopy as a powerful tool for determining the multiplicity of transition metals in photochemical reactions of coordination complexes.
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