Ultralow Lattice Thermal Conductivity in Double Perovskite Cs₂PtI₆: A Promising Thermoelectric Material

Abstract

We report first-principle calculations of the recently synthesized Pb-free double perovskite Cs 2 PtI 6 , which we found to have the potential to be an excellent thermoelectric material, through the investigation of its electronic and phonon transport properties. The Heyd−Scuseria−Ernzerhof functional results in an indirect band gap of 1.40 eV, perfectly matching the experiment. Our well-converged phonon dispersion displays positive frequencies in the entire Brillouin zone and hence confirms the dynamic stability of the material. Further, the low-lying optical modes mix significantly with the heat-carrying acoustic phonons and add to their scattering phase space. We have found strong phonon anharmonicity due to the nonsymmetric and nonspherical electron densities of the atoms derived from their bonding environment, which in combination with low group velocities and high phonon scattering rates results in ultralow lattice thermal conductivity in Cs 2 PtI 6 . For example, it is 0.15 W/mK at 300 K, which is 8-fold smaller than that reported for the typical thermoelectric material Bi 2 Te 3 . Our simulations show that it could be reduced by another factor of 2 by nanostructuring the material with features of around 8 nm. We have found a remarkably high p-type Seebeck coefficient of 139 μV/K at the maximum considered carrier concentration and temperature. Our calculations also find a high figure of merit of 1.03 for the p-type carriers at room temperature, attributed to the substantial thermoelectric coefficient S 2 σ/τ, where S, σ, and τ are the Seebeck coefficient, the electrical conductivity, and the relaxation time, respectively.

New lead‐free double perovskites X 2 GeI 6 (X = K, Rb, Cs) for solar cells, and renewable energy as an alternate of hybrid perovskites

“…At 300 K, the reported values of κ l are 0.11 W/mK, 0.13 W/mK, and 0.17 W/mK, which is extremely low and consistent with already reported Cs 2 PdI 6 (0.15 W/mK) 48 . These values are ultralow as compared to existing thermoelectric players, for example, 1.24 W/mK (Bi 2 Te 3 ), 49 2.60 W/mK (GeTe), 1.50 W/mK (PbSe 0.5 Te 0.5 ), 1.60 W/mK (Sb 2 Te 3 ), 50 1.19 W/mK (SnSe), 2.20 W/mK (PbSe), 51 1.20 W/mK (Ge 2 Sb 2 Te 5 ), 2.00 W/mK (PbTe), 52 etc. Therefore, the studied materials our considered promising materials for thermoelectric applications.…”

First principle study of lead‐free double perovskites halidesRb2Pd(Cl/Br)6for solar cells and renewable energy devices: A quantumDFT

“…42 3.3 | Band structures and density of statesThe Band structure (BS) and density of states (DOS) for variant perovskite halides Rb 2 PdCl 6 and Rb 2 PdBr 6 have been calculated to explore them for energy applications. The energy band structure for Rb 2 PdCl 6 and Rb 2 PdBr 6 has been computed along the density of state in the first Brillouin zone as shown in Figure3A,B.…”

Ultralow lattice thermal conductivity at room temperature in 2D KCuSe from first-principles calculations

“…Monolayer KCuSe has six atoms per primitive cell, so there are eighteen phonon branches in the phonon spectrum. The maximum frequency of phonon branches reaches 5.06 THz, which is slightly higher than that of monolayer KAgSe (∼4.76 THz), 24 but lower than that of Cs 2 PtI 6 (∼5.11 THz) 33 and monolayer CdPSe 3 (∼13.2 THz). 34 Three acoustic phonon branches are colored.…”

“…For most materials, the lattice thermal conductivity versus temperature follows κ ∼ 1/ T α (0.85 ≤ α ≤ 1.05), and our results are consistent with the conventional κ ∼ 1/ T relationship. 37 The most striking thing is that the lattice thermal conductivity is shown to be unprecedentedly low over the entire temperature range, reaching merely 0.021 W m −1 K −1 at 300 K, which is substantially lower than those of monolayer KAgSe (0.26 W m −1 K −1 ), 24 monolayer TlCuSe (0.44 W m −1 K −1 ), 26 Cs 2 PtI 6 (0.15 W m −1 K −1 ), 33 and monolayer AgSbSe 2 (0.48 W m −1 K −1 ). 38 To analyze the contribution of the acoustic and optical phonons to the lattice thermal conductivity, we calculate the dependence of the cumulative lattice thermal conductivity versus frequency at room temperature.…”