Research seminars in physics
Next seminars:
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Monday, 24.February 2025, 9:15-10:00, room 21D304
Title: From model system to devices – Gaining insight into solar cells with photoelectron spectroscopy
Speaker: Ute Cappel, Dept. Physics & Astronomy, X-ray Photon Science division, Uppsala University
Abstract:
Solar cells have a great potential in replacing fossil fuels in electricity generation, if requirements of low production costs can be met. In the last years, lead halide perovskites have drastically changed the solar cell research field due to their ease of synthesis and high power conversion efficiencies, which now reach over 25%. The future success of these developments crucially depends on understanding the details charge separation, charge transport and charge recombination at the interfaces between the different layers in a solar cell as well as what parameters limit solar cell stability.
X-ray based techniques such as photoelectron spectroscopy (PES) are powerful tools for obtaining electronic structure information of materials at an atomic level. By varying the photon energy from soft to hard X-rays, photoelectron spectroscopy can be used for non-destructive depth profiling of the solar cell interfaces giving information about the energy alignment and chemical structure and composition at the interface. Furthermore, time-resolved photoelectron spectroscopy can be used to investigate dynamics within devices relating to charge transport and material stability.
In this presentation, I will discuss how we have used photoelectron spectroscopy to gain fundamental insights into materials for solar cells by carrying out investigations ranging from single crystal model systems to real devices and moving from static to dynamic, time-resolved measurements.
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Thursday, 27.February 2025, 14:15-15:00, room 21A342 (Eva Eriksson)
Title: (Hard) X-ray based electron spectroscopy and core-hole clock spectroscopy
Speaker: Andreas Lindblad, Dept. Physics & Astronomy, X-ray Photon Science division, Uppsala University
Abstract:
I will discuss our recent work on electron spectroscopy of polymer systems containing sulphur, in particular how the samples evolve upon x-ray illumination.
Using resonant Auger spectroscopy around the sulphur K-edge we have studied several polymer systems to infer charge transfer rates from the core-excited state[1,2]. I will discuss the methodology using a model system (Xenon adsorbed on noble metals) [3] and how the theory for core hole clock spectroscopy develop currently.
The information rate provided by angular resolved time-of-flight (ArTOF) spectrometers combined with a dipole soft X-ray synchrotron source (at the PM4 beamline at HZB/Berlin) allows us to map the spectral evolution in short enough time-increments. This gives a glimpse into what can happen to the sample during the first sweep at an undulator beamline.
I will also present the suggested SpectraWISE beamline at MAX IV that will provide X-rays in the tender regime (2-14 keV) for electron spectroscopies. With both UHV and ambient pressure end stations it could serve the Swedish spectroscopy community and serve as a platform for applied and fundamental material science, low density matter studies and catalysis.
[1] Johansson, Fredrik. O. L., et al. "Femtosecond and attosecond electron-transfer dynamics in PCPDTBT: PCBM bulk heterojunctions." The Journal of Physical Chemistry C 122.24 (2018): 12605-12614.
[2] Berggren, Elin, et al. "Charge Transfer in the P (g42T-T): BBL Organic Polymer Heterojunction Measured with Core-Hole Clock Spectroscopy." The Journal of Physical Chemistry C 127.49 (2023): 23733-23742.
[3] Johansson, Fredrik OL, et al. "Resonant Auger spectroscopy on solid xenon on gold, silver, and copper substrates." Physical Review A 107.3 (2023): 032802.