Perovskite‐Related 2D Compounds in the System 5‐Amino Valerian Acid Cation/MA/Pb/X (X = Cl, Br) – Synthesis, Crystal Structures, and Optical Properties

Abstract

Perovskite‐related 2D‐compounds of the series 5‐AVA2MAn–1PbnBr3n–1 were synthesised and characterised for the representatives with n = 1, 2, and 3 [5‐AVA = 5‐amino valerian acid cation, HOOC(CH2)4NH3+]. In addition, we have investigated the chloride compound 5‐AVA2PbCl4 and the binary compounds 5‐AVAX (X = Cl, Br). The crystal structures of the 2D compounds represent well‐known cut‐outs of the cubic 3D perovskites with layers of corner‐sharing PbBr6 octahedrons in (100) orientation. According to the value of n the layer thickness comprises one, two or three layers. Similar to most of the perovskite‐related representatives the PbBr6 octahedrons are rotated, but with slight differences. We have analysed the rotation pattern with respect to the different aspects of hydrogen bonding and orientation of the organic cations 5‐AVA+ and MA+. Measurements of the optical properties reveal a decrease of the band gap from 3.02 eV (n = 1) over 2.80 eV (n = 2) to 2.70 eV (n = 3). For 5‐AVA2PbBr4 we observed strong blue fluorescence (413 nm) with a remarkably small Strokes shift (47 nm). All investigations were influenced by the reduced stability of the representatives with n = 2 and n = 3 with respect to the degradation into the simpler compounds 5‐AVA2PbBr4 and MAPbBr3. This is in contrast to similar 2D‐iodides, where many representatives are known and n can reach values up to 6 and 7. Our series with n = 1, 2, and 3 represent the third example for a series of compounds with n = 1–3.

Crystal Structures of the Perovskite‐Related System A/Rb/Cu(II)/Br (A=BA, Gu, PEA, 5‐AVA, H2en) with Winners, Losers and Compromises – Versatility from 0D to 3D on Different Levels

“…One of the H‐atoms forms a short H‐bridge, the second one an intermediate, and the third one two or three weak bridges. The 5‐AVA cations are dimerized by the O−H hydrogen bonds of the carboxylic groups, as was already found for the corresponding Pb(II) compound [28] …”

“…The 5-AVA cations are dimerized by the OÀ H hydrogen bonds of the carboxylic groups, as was already found for the corresponding Pb(II) compound. [28] Because of the large size of the 5-AVA cations and the additional H-bridges of the carboxyl group, the relative arrangement of the CuBr x layers can't be easily compared to the other 2D compounds. Hence, the classification as a RP-Phase or an ACI/HD-phase [10a] is not appropriate, in contrast to representatives with smaller organic cations.…”

From 1D to 3D: Perovskites within the System HSC(NH2)2I/CH3NH3I/PbI2 with Maintenance of the Cubic Closest Packing

“…With very large and/or long cations, the differentiation between the RP and ACI/HD phases becomes meaningless with respect to the lattice parameters and Bravais lattice, for example, with 5-aminovaleric acid, which forms different types of dimers by H bridges via the COOH groups . A similar situation results when the terminal anions are not spherical like in MA 2 PbI 2( SCN) 2 …”

Shedding Light on the Stability and Structure–Property Relationships of Two-Dimensional Hybrid Lead Bromide Perovskites

“…A few results nevertheless indicate that optical tunability and homogeneous emission lines may be obtained when using halide binary alloys thanks to the robustness of the 2D Wannier exciton for the [100] orientation . Synthetically, the majority of the materials reported are monolayer ( n = 1) 2D bromide perovskites. ,− A significant amount of the studied monolayer lead bromide perovskites adopt the [110] orientation, which exhibit broadband emission due to photogenerated energy distribution of self-trapped exciton states that are associated with the distortion of the [110] corrugated structure. − …”