Ultrafast photo-induced phonon hardening due to Pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites

Xia, Chelsea Q;Poncé, Samuel;Peng, Jiali;Ulatowski, Aleksander M;Johnston, Michael B;et.al.
(2021) Journal of Physics: Materials — Vol. 4, n° 4, p. 44017 (2021)

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Authors
  • Xia, Chelsea Qorcid-logoDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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  • Poncé, Samuelorcid-logoUCLouvain
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  • Peng, JialiKey Lab of Artificial Micro- and Nano-Structures of Ministry of Education of China, School of Physics and Technology, Wuhan University, Wuhan 430072, People’s Republic of China
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  • Ulatowski, Aleksander MDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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  • Johnston, Michael Borcid-logoDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
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Abstract
Metal-halide perovskite semiconductors have attracted intense interest over the past decade, particularly for applications in photovoltaics. Low-energy optical phonons combined with significant crystal anharmonicity play an important role in charge-carrier cooling and scattering in these materials, strongly affecting their optoelectronic properties. We have observed optical phonons associated with Pb–I stretching in both MAPbI3 single crystals and polycrystalline thin films as a function of temperature by measuring their terahertz conductivity spectra with and without photoexcitation. An anomalous bond hardening was observed under above-bandgap illumination for both single-crystal and polycrystalline MAPbI3. First-principles calculations reproduced this photo-induced bond hardening and identified a related lattice contraction (photostriction), with the mechanism revealed as Pauli blocking. For single-crystal MAPbI3, phonon lifetimes were significantly longer and phonon frequencies shifted less with temperature, compared with polycrystalline MAPbI3. We attribute these differences to increased crystalline disorder, associated with grain boundaries and strain in the polycrystalline MAPbI3. Thus we provide fundamental insight into the photoexcitation and electron–phonon coupling in MAPbI3.
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Xia, C. Q., Poncé, S., Peng, J., Ulatowski, A. M., Patel, J. B., Wright, A. D., Milot, R. L., Kraus, H., Lin, Q., Herz, L. M., Giustino, F., & Johnston, M. B. (2021). Ultrafast photo-induced phonon hardening due to Pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites. Journal of Physics: Materials, 4(4), 44017. https://doi.org/10.1088/2515-7639/ac22b9 (Original work published 2021)