Mi, 19.05.2021  |  14:00 Uhr
Virtual, via Zoom link
MBI Colloquium

Charge carrier dynamics in perovskites and transition metal oxides

Prof. Dr. Majed Chergui | Laboratoire de Spectroscopie Ultrarapide and Lausanne Centre for Ultrafast Science, ISIC, Lausanne, Switzerland

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I will present our recent studies on the electronic structure and charge carrier dynamics in lead-halide perovskites and in transition metal oxides, based on the use of a variety of experiment tools, such ultrafast transient optical absorption spectroscopy, ultrafast angle-resolved photoelectron spectroscopy (ARPES), picosecond X-ray absorption spectroscopy (XAS), etc. I will show how steady-state ARPES can be used to reveal the occurrence of hole polarons in CsPbBr3.[1] These were previously suggested by ps X-ray absorption spectroscopy[2] but not quantified. Further studies by ps XAS allow us to also disentangle light-induced thermal and electronic effects in CsPbBr3.[3] The study of organic lead-halide perovskites under high pump fluences reveals the occurrence of the long-predicted Mahan excitons, which appear above the Mott transition of the solid.[4] We also show that the very popular anatase TiO2 material, whose first exciton shows remarkable stability against defects, impurities, temperature, etc.,[5] is also found to have the highest critical density for the Mott transition ever reported in semiconductors.[6] Finally, I will introduce a novel tool for the study of transport phenomena at the nanoscale, which consists of fs hard X-ray transient grating spectroscopy.[7],[8]

[1]Valence Band Mapping of CsPbBr3 Perovskite Single Crystals by Angle-Resolved Photoemission Spectroscopy

M. Puppin et al, Physical Review Letters 124 (2020) 206402

[2]Localized holes and delocalized electrons in photoexcited inorganic perovskites: Watching each atomic actor by picosecond X-ray absorption spectroscopy

F. G. Santomauro et al, Structural Dynamics 4 (2017) 044002

[3]Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskites Nanocrystals

O. Cannelli et al, Journal of the American Chemical Society (under review)

[4]Mahan excitons in room temperature organic-inorganic lead-based perovskites

T. Palmieri et al, Nature Communications 11 (2020) 850

[5]Strongly bound excitons in anatase TiO2 single crystals and nanoparticles
E. Baldini et al, Nature Communications 8 (2017) 13

[6]Giant Exciton Mott Density in Anatase TiO2

E. Baldini et al, Physical Review Letters 125 (2020) 116403

[7]Towards X-ray Transient Grating Spectroscopy

C. Svetina et al, Optics Letters 44 (2019) 574

[8]Hard X-ray Transient Grating Spectroscopy on Bismuth Germanate

J. R. Rouxel et al, Nature Photonics (https://doi.org/10.1038/s41566-021-00797-)

 

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