Institute of High Pressure Physics

Lead halide perovskites are known as efficient materials for solar cells, LED’s, lasers, photodetectors and even γ-detectors. Recently, this long list of applications has been updated by the piezoelectric devices.

New publication in ACS Energy Letters (IF=22) titled „The Impact of Piezoelectricity in Low Dimensional Metal Halide Perovskite” S. Rahmany, A. Shpatz Dayan, M. Wierzbowska, A. J. Ong, Y. Li, S. Magdassi, A. I. Y. Tok and L. Etgar, ACS Energy Letters, 1527, 2024 doi: 10.1021/acsenergylett.4c00177 rised with a theoretical contribution from Unipress and joint experimental work in Jerusalem and Singapore

The quasi-2D lead halide provskite with the organic cation, methylammonium (MA), has been synthesized with three types of the so-called barrier molecules:  linear barrier (BuDABr = butyl diamine bromide, (A)) with two amine groups, an aromatic barrier with a short-chain residue (BzABr = benzyl amine bromide, B)), and an aromatic barrier containing an additional carbon in the chain residue (PEABr = phenylethylammonium   bromide, (C)). The perovskite layers in the above sandwiches have been prepared in four thickness values: n=1, 5, 10 and 50. Moreover, each perovskite composition was mixed with polyvinylidene fluoride (PVDF) to form perovskite:PVDF composite in a ratio of 25:75.

Measurements reveal the largest piezoelectric response from the composites with BuDA barrier molecules (see the amplitudes below for the case n=5).

Large advanced theoretical simulations (with 300 atoms!) by means of ab initio many body perturbation theory approach with the random phase approximation were done by Małgorzata Wierzbowska for the dielectric function components, in-plane (ϵ^║) and out-of-plane (ϵ^┴), defined as:

and allowed to obtain the material polarizabilities (α), at a few crystal directions (q).

A good agreement with the experimental trend can be seen the Table 1.

However, the mechanism of this effect is not due to the molecular polarizabilies, that are reversely proportional to the total trend! Also the barrier molecules that contain the phenyl ring are placed in this composite as a double layer (symmetrically rotated) that cancels the molecular contributions, due to the Ruddlesden-Popper structure. The main cause of the piezoelectric effect is a distortion of perovskite layers triggered by molecular parts with the amino groups. Embedding this group to perovskite piramids is the largest for the linear barrier, BuDA, while the aromic rings of BzA and PEA interact strongly with each other preventing the elastic effects to show up with the stronger amplitudes.

Read more in the original paper "The Impact of Piezoelectricity in Low Dimensional Metal Halide Perovskite"