Non-monotonic Thermal Conductivity of FAxMA1-xPbI3 Achieving Ultralow Values: The Role of Anharmonic Low Energy Rotation of Organic Moieties

Pariari, D and Acharyya, P and Sinha, A and Mohanty, A and Sett, S and Gill, NK and Ghosh, A and Waghmare, UV and Biswas, K and Sarma, DD (2024) Non-monotonic Thermal Conductivity of FAxMA1-xPbI3 Achieving Ultralow Values: The Role of Anharmonic Low Energy Rotation of Organic Moieties. In: ACS Energy Letters, 9 . pp. 2128-2136.

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Abstract

Stability issues of MAPbI3 and FAPbI3 have led to the exploration of more stable FAxMA1-xPbI3 solid solutions for many energy applications. Thermal properties are important in view of the inevitable heat generation in energy conversion processes. MAPbI3 is reported to have an ultralow thermal conductivity, κ (�0.34 W·m-1·K-1). Surprisingly, there is no report of κ for FA/MA mixed compositions, despite their obvious relevance. Here, we report an intriguing observation of a non-monotonic reduction of κ with FA substitution, while most other physical properties, such as the lattice parameters and bandgap, vary monotonically. This leads the asymmetric composition FA0.3MA0.7PbI3 to become the lowest κ (�0.2 W·m-1·K-1) material among all three-dimensional metal halide perovskites. We show this non-monotonic κ is a consequence of two monotonic and opposing trends with increasing FA compositions, namely, an increasingly facile rotation of a decreasing number of MA ions. Raman studies, together with ab initio theoretical results, show that the heterogeneous bonding environment in FAxMA1-xPbI3 results in numerous low-energy, highly anharmonic, and localized optical phonon modes strongly coupled to acoustic phonons related exclusively to MA, but not FA, rotations, leading to very short phonon lifetimes (0.3-2 ps) and, therefore, to the ultralow κ for these compounds. © 2024 American Chemical Society.

Item Type:	Journal Article
Publication:	ACS Energy Letters
Publisher:	American Chemical Society
Additional Information:	The copyright for this article belongs to American Chemical Society.
Keywords:	Metal halides; Perovskite; Phonons, reductions; Anharmonic; Conversion process; Energy applications; Halide perovskites; Low κ; Lower energies; Monotonics; Organic moiety; Stability issues, Thermal conductivity
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering Division of Physical & Mathematical Sciences > Physics
Date Deposited:	28 Aug 2024 11:33
Last Modified:	28 Aug 2024 11:33
URI:	http://eprints.iisc.ac.in/id/eprint/84845

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