Berlin 2024 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 35: THz and MIR
HL 35.1: Vortrag
Mittwoch, 20. März 2024, 15:00–15:15, EW 203
Observation of picosecond Polaron Stabilization in FA-lead-halide pervoskites via infrared modes — •Daniel Sandner1, Matthias Nuber1, Qi Ying Tan2, Reinhard Kienberger1, Cesare Soci2, and Hristo Iglev1 — 1Chair for Laser- and X-ray physics E11, Technische Universität München, Garching, Germany — 2Centre for Disruptive Photonic Technologies, NTU, Singapore
The optoelectronic properties of lead-halide perovskites are greatly influenced by the polarons. In our experiments, we use time-resolved mid-infrared spectroscopy with sub-ps and single wavenumber resolution to study the vibrational properties of the FA cation via a CN stretching mode. It has been shown in polymers and perovskites that localized charge carriers can lead to infrared active (IRAV) modes. After exciting Cs0.2FA0.8PbBr3 films with visible light pulses, we observe an IRAV mode that increases up to 100 ps after excitation in intensity, while the broad background by free carrier absorption shows a decline by carrier recombination. We interpret this finding as Polaron stabilization, meaning the rearrangement of the polar lattice around the charge carrier. (doi.org/10.1039/D2TC04519B)
We further studied the role of the halide, temperature, and confinement. At low temperatures, the IRAV mode, which we associate with a polaron, is weaker and shows shorter distinct dynamics, which is in good agreement with reported transport data. We find that the effect is absent in quasi-2D perovskites, which adds more experimental evidence to the recent debate about the nature of photoexcitations in those materials.
Keywords: lead-halide Perovskite; Polaron; IRAV mode; mIR pump-probe; time-resolved infrared spectroscopy