Ultralow Thermal Conductivity of Two-Dimensional Metal Halide Perovskites

Abstract

We report on the thermal conductivities of two-dimensional metal halide perovskite films measured by time domain thermoreflectance. Depending on the molecular substructure of ammonium cations and owing to the weaker interactions in the layered structures, the thermal conductivities of our two-dimensional hybrid perovskites range from 0.10 to 0.19 W m–1 K–1, which is drastically lower than that of their three-dimensional counterparts. We use molecular dynamics simulations to show that the organic component induces a reduction of the stiffness and sound velocities along with giving rise to vibrational modes in the 5–15 THz range that are absent in the three-dimensional counterparts. By systematically studying eight different two-dimensional hybrid perovskites, we show that the thermal conductivities of our hybrid films do not depend on the thicknesses of the organic layers and instead are highly dependent on the relative orientation of the organic chains sandwiched between the inorganic constituents.

Enhancing Thermoelectric Power Factor of 2D Organometal Halide Perovskites by Suppressing 2D/3D Phase Separation

“…However, the measurement of the thermal conductivity of solution‐processed thin films is difficult. Since the electron‐crystal/phonon‐glass behavior of OHP crystal [ 9–11 ] endows conventional OHP films with ultralow thermal conductivities ≈0.5 W m −1 K −1 , [ 18,61,62 ] the thermal conductivity of the RP 2D OHPs was also expected to be around 0.5 W m −1 K −1 , which resulted in ZT of 0.07.…”

“…[ 1–8 ] Recently, OHPs have received fresh attention as thermoelectric (TE) materials because their unique organic–inorganic hybrid crystal structure endows them with electron‐crystal phonon‐glass behavior, where the inorganic frameworks of OHPs efficiently conduct charge carriers, whereas loosely bound organic molecules scatter phonons via a cluster‐rattling mechanism. [ 9–11 ] Such electronic and thermal properties of OHPs are beneficial to the TE figure‐of‐merit ZT = S 2 σT /κ, where S [µV K −1 ] is the Seebeck coefficient, σ [S cm −1 ] is the electrical conductivity, T [K] is the absolute temperature, and κ [W m −1 K −1 ] is thermal conductivity. However, TE applications of OHPs have been limited because the low carrier concentration ρ of OHPs produces a relatively low σ and, consequently, a low power factor S 2 σ. Intrinsic charge carriers in OHPs are generated from defects, and defect formation in OHPs is suppressed by ionic compensation of charged point defects and by the defect‐tolerant electronic structure.…”

Ultralow thermal conductivity via topological network control of vibrational localization in amorphous chalcogenides

“…Using the Packmol routine 45 as implemented in QuantumATK 46 , we create ten different initial atomic configurations by packing 60 of these SiTe 4 units in a supercell. The volume of the supercell is determined by the measured mass density 47 (5.08 g/cm 3 ). Structural relaxation of the system is then performed to reach the minimum energy configuration.…”

“…In recent years, there have been numerous efforts to synthesize materials with ultralow thermal conductivities, a crucial parameter in the development of thermoelectric materials, memory devices, and thermal barrier coatings [1][2][3] . It has been generally believed that amorphous solids possess the lowest thermal conductivity possible 4 .…”

New accurate molecular dynamics potential function to model the phase transformation of cesium lead triiodide perovskite (CsPbI3)

“…25 The use of MYP was not limited to 3D structures, it was also used to study the thermal conductivity of 2D MAPbI 3 thin lms. 26 However, the resulted volume as a function of temperature curve from the MYP has discrepancies when compared to the experimental results because of the fact that the model ignored the charge redistribution and the covalent nature of lead iodide interactions. 16 Hata et al 6 studied MAPbBr 3 using the same MYP potential developed by Mattoni et al 16 They used the same Pb-Pb, Pb-MA, and MA internal interactions as in MAPbI 3 .…”