Tuning the Structural Rigidity of Two-Dimensional Ruddlesden–Popper Perovskites through the Organic Cation

Abstract

Two-dimensional (2D) hybrid organic–inorganic perovskites are an interesting class of semi-conducting materials. One of their main advantages is the large freedom in the nature of the organic spacer molecules that separates the individual inorganic layers. The nature of the organic layer can significantly affect the structure and dynamics of the 2D material; however, there is currently no clear understanding of the effect of the organic component on the structural parameters. In this work, we have used molecular dynamics simulations to investigate the structure and dynamics of a 2D Ruddlesden–Popper perovskite with a single inorganic layer ( n = 1) and varying organic cations. We discuss the dynamic behavior of both the inorganic and the organic part of the materials as well as the interplay between the two and compare the different materials. We show that both aromaticity and the length of the flexible linker between the aromatic unit and the amide have a clear effect on the dynamics of both the organic and the inorganic part of the structures, highlighting the importance of the organic cation in the design of 2D perovskites.

Layered Hybrid Formamidinium Lead Iodide Perovskites: Challenges and Opportunities

“…Thus, bulky adamantyl-based spacers show a less pronounced templating effect toward a cubic phase compared with other spacers featuring longer alkyl chains, despite their stronger van der Waals interactions in the spacer layer. ,, This interplay between the spacer and the inorganic framework was further assessed by comparing the thickness of the spacer layer ( d 1 ) and the distance between the adjacent spacers ( d 2 ) (Figure b,d). As ADAM spacers did not show a clear trend, this corroborates a less pronounced templating effect in comparison with other alkyl-chain-containing moieties, such as AVA and BA cations. ,,,, As a result, FA/ADAM-based n > 1 compositions featured a mixture of α- and δ-FAPbI 3 phases. , This is likely to be the result of steric effects and the anisotropic dynamics of the ADAM spacer molecules, which are likely to contribute to the structural distortion. ,− Specifically, the tumbling of the spacer was found to be slightly anisotropic in the layered ADAM/FA-based structures with a reorientation time on the order of nanoseconds, which was evidenced by variable-temperature 2 H NMR spectroscopy and MD simulations. , On the contrary, MD simulations of (PDMA)­FA n –1 Pb n I 3 n +1 (Figure e) show a transition from a mixed DJ–RP intermediate to a DJ structure at higher temperatures above 350 K, approaching a near-ideal DJ structure with the increasing number of layers ( n ). Unlike alkyl-based spacers, aromatic PDMA adopts T-shaped and parallel-displaced π interactions, contributing to a more rigid framework. ,,, In accordance with the RP phases, the increasing n is accompanied with an increased penetration depth and a decrease of the corresponding N···Pb distances.…”

Manipulating Color Emission in 2D Hybrid Perovskites by Fine Tuning Halide Segregation: A Transparent Green Emitter

“…Furthermore, recently reported theoretical calculations confirm that the length of the carbon chain has an influence over the rigidity of the spacing moieties, and the equilibrium position that lead and halide atoms assume in the inorganic octahedra can vary accordingly. [ 28 ] It is widely known that hybrid perovskites exhibit unique properties of softness, in which the chemical bonding between metal halide octahedral frameworks and cations is governed by weak ionic and hydrogen bonding. [ 29,30 ] The steric hindrance provided by bulky cations such as TEA and TMA therefore play a role: TMA has one methyl group, while TEA has one longer methyl group.…”

“…can vary accordingly. [28] It is widely known that hybrid perovskites exhibit unique properties of softness, in which the chemical bonding between metal halide octahedral frameworks and cations is governed by weak ionic and hydrogen bonding. [29,30] The steric hindrance provided by bulky cations such as TEA and TMA therefore play a role: TMA has one methyl group, while TEA has one longer methyl group.…”

Crystal structure prediction of (quasi-)two-dimensional lead halide perovskites

“…Following previous work, [24][25][26][27][28] and in particular the idea behind MAPI family of potential developed by Mattoni et al, 26,27 we undertake an approach where the total classical potential is modeled as a sum of i) nonbonding potential that depends only on the interatomic distances with only two-body terms taken into account and ii) a bonding potential including bonds, dihedrals, and angles as described by GAFF, 29 a generalization of the AMBER 30 force field.…”

“…E.g., classical potentials for Q2DPs containing iodine instead of bromide can be constructed in a completely analogous manner as described in Section 2.2, but using the parameters for MAPbI 3 . 26,28 As detailed in an another work, 22 we employed GO-MHALP to predict a mixed halide structure. We use the Berthelot rule to calculate the Buckingham parameters for Pb − Pb and Br − I interactions:…”