Supercompliant and Soft (CH3NH3)3Bi<

Abstract

In this letter, we show the phonon dispersion of (CH 3 NH 3) 3 Bi 2 I 9 single crystals at 300K as deduced from high energy resolution inelastic x-ray scattering measurements. The frequencies of acoustic phonons are among the lowest of all the reported crystals. Nanoindentation measurements verified that these crystals are very compliant and considerably soft. The frequency overlap between acoustic and optical phonons results in strong acousticoptical scattering. All these features lead to an ultralow thermal conductivity. The fundamental knowledge obtained from this study will accelerate the design of novel hybrid materials for energy applications.

Halide Perovskites: Thermal Transport and Prospects for Thermoelectricity

“…Compared to 3D perovskites, lower κ is observed in the case of 0D perovskites such as (MA) 3 Bi 2 I 9 and Cs 4 PbCl 6 . [ 93,94,119 ] Discrete octahedra structure with low group velocities, reduced phonon lifetimes, and the localization of vibrational energy leads to the ultralow κ in 0D perovskites. [ 64,93 ]…”

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.…”

Scalable Production of Ambient Stable Hybrid Bismuth‐Based Materials: AACVD of Phenethylammonium Bismuth Iodide Films**

“…These structural differences are thought to be the cause of the lower absorption coefficient and the uniquely low thermal conductivity of [CH 3 NH 3 ] 3 [Bi 2 I 9 ], otherwise a key feature for the design of thermoelectric devices. [32,34] To fully under-stand design limitations of PSCs, a better understanding of the underlying structure-property relationships is still necessary, hence fabrication methods that yield defect-free, compact and homogeneous films should be developed. [27] Varied approaches such as cation displacement, [36] vapor assisted solution process [30] and anti-solvent assisted crystallization solution process [37] have successfully managed to improve film coverage and achieve a smooth morphology.…”

“…A substantial intrinsic difference between lead and bismuth‐based hybrid materials lies within their crystal structures: while CH 3 NH 3 PbI 3 has 3D structure of corner‐sharing octahedra (perovskite structure, Figure 1a), [13] [CH 3 NH 3 ] 3 [Bi 2 I 9 ] exhibit a derived 0D array of disconnected face‐sharing octahedra [33] (Figure 1b). These structural differences are thought to be the cause of the lower absorption coefficient and the uniquely low thermal conductivity of [CH 3 NH 3 ] 3 [Bi 2 I 9 ], otherwise a key feature for the design of thermoelectric devices [32,34] . To fully understand design limitations of PSCs, a better understanding of the underlying structure‐property relationships is still necessary, hence fabrication methods that yield defect‐free, compact and homogeneous films should be developed [27] …”

“…These structural differences are thought to be the cause of the lower absorption coefficient and the uniquely low thermal conductivity of [CH 3 NH 3 ] 3 [Bi 2 I 9 ], otherwise a key feature for the design of thermoelectric devices. [ 32 , 34 ] To fully understand design limitations of PSCs, a better understanding of the underlying structure‐property relationships is still necessary, hence fabrication methods that yield defect‐free, compact and homogeneous films should be developed. [27] …”