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O: Fachverband Oberflächenphysik
O 88: Focus Session: Ultrafast Processes in Organic Semiconductors and Perovskites II (joint session O/CPP)
O 88.8: Vortrag
Donnerstag, 21. März 2024, 17:00–17:15, MA 004
Direct observation of ultrafast lattice distortions during exciton-polaron formation in lead halide perovskite nanocrystals — •Hélène Seiler1,2, Zahn Daniela1, Victoria C.A. Taylor1, Maryna I. Bodnarchuk3, Yoav W. Windsor1,4, Maksym V. Kovalenko3,5, and Ralph Ernstorfer1,4 — 1Fritz Haber Institute, Berlin, Germany — 2Freie Universität Berlin, Berlin, Germany — 3EMPA, Dübendorf, Switzerland — 4Technische Universität Berlin, Berlin, Germany — 5ETHZ, Zürich, Switzerland
We have employed femtosecond electron diffraction (FED) to directly measure the sub-picosecond lattice dynamics of weakly confined CsPbBr3 nanocrystals following above-gap photoexcitation. The data reveal a light-induced structural distortion appearing on a time scale varying between 380 and 1200 fs depending on the excitation fluence. We attribute these dynamics to the effect of exciton-polarons on the lattice and the slower dynamics at high fluences to slower sub-picosecond hot-carrier cooling, which slows down the establishment of the exciton-polaron population. Further analysis and simulations show that the distortion is consistent with motions of the [PbBr3]- octahedral ionic cage, and closest agreement with the data is obtained for Pb-Br bond lengthening.
Keywords: lead halide perovskties; femtosecond electron diffraction; ultrafast; nanocrystals; exciton-polaron