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Issue 10, 2020
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Vibrational dynamics in lead halide hybrid perovskites investigated by Raman spectroscopy

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Abstract

Lead halide perovskite semiconductors providing record efficiencies of solar cells have usually mixed compositions doped in A- and X-sites to enhance the phase stability. The cubic form of formamidinium (FA) lead iodide reveals excellent opto-electronic properties but transforms at room temperature (RT) into a hexagonal structure which does not effectively absorb visible light. This metastable form and the mechanism of its stabilization by Cs+ and Br incorporation are poorly characterized and insufficiently understood. We report here the vibrational properties of cubic FAPbI3 investigated by DFT calculations on phonon frequencies and intensities, and micro-Raman spectroscopy. The effects of Cs+ and Br partial substitution are discussed. We support our results with the study of FAPbBr3 which expands the identification of vibrational modes to the previously unpublished low frequency region (<500 cm−1). Our results show that the incorporation of Cs+ and Br leads to the coupling of the displacement of the A-site components and weakens the bonds between FA+ and the PbX6 octahedra. We suggest that the enhancement of α-FAPbI3 stability can be a product of the release of tensile stresses in the Pb–X bond, which is reflected in a red-shift of the low frequency region of the Raman spectrum (<200 cm−1).

Graphical abstract: Vibrational dynamics in lead halide hybrid perovskites investigated by Raman spectroscopy

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Article information


Submitted
04 Dec 2019
Accepted
31 Jan 2020
First published
26 Feb 2020

This article is Open Access

Phys. Chem. Chem. Phys., 2020,22, 5604-5614
Article type
Paper

Vibrational dynamics in lead halide hybrid perovskites investigated by Raman spectroscopy

J. Ibaceta-Jaña, R. Muydinov, P. Rosado, H. Mirhosseini, M. Chugh, O. Nazarenko, D. N. Dirin, D. Heinrich, M. R. Wagner, T. D. Kühne, B. Szyszka, M. V. Kovalenko and A. Hoffmann, Phys. Chem. Chem. Phys., 2020, 22, 5604
DOI: 10.1039/C9CP06568G

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