Dynamic Nanodomains Dictate Macroscopic Properties in Lead Halide Perovskites (2404.14598v2)

Abstract: Empirical A-site cation substitution has advanced the stability and efficiency of hybrid organic-inorganic lead halide perovskites solar cells and the functionality of X-ray detectors. Yet, the fundamental mechanisms underpinning their unique performance remain elusive. This multi-modal study unveils the link between nanoscale structural dynamics and macroscopic optoelectronic properties in these materials by utilising X-ray diffuse scattering, inelastic neutron spectroscopy and optical microscopy complemented by state-of-the-art machine learning-assisted molecular dynamics simulations. Our approach uncovers the presence of dynamic, lower-symmetry local nanodomains embedded within the higher-symmetry average phase in various perovskite compositions. The properties of these nanodomains are tunable via the A-site cation selection: methylammonium induces a high density of anisotropic, planar nanodomains of out-of-phase octahedral tilts, while formamidinium favours sparsely distributed isotropic, spherical nanodomains with in-phase tilting, even when crystallography reveals cubic symmetry on average. The observed variations in the properties of dynamic nanodomains are in agreement with our simulations and are directly linked to the differing macroscopic optoelectronic and ferroelastic behaviours of these compositions. By demonstrating the influence of A-site cation on local nanodomains and consequently, on macroscopic properties, we propose leveraging this relationship to engineer the optoelectronic response of these materials, propelling further advancements in perovskite-based photovoltaics, optoelectronics, and X-ray imaging.

• The paper reveals how dynamic nanodomains, influenced by A-site cation selection, modulate the optoelectronic and ferroelastic properties of lead halide perovskites.
• It employs X-ray diffuse scattering, inelastic neutron spectroscopy, and machine learning-assisted MD simulations to capture nanoscale dynamics accurately.
• Findings indicate that MA forms dense planar domains while FA results in sparser spherical ones, driving distinct material behaviors.

Overview of "Dynamic Nanodomains Dictate Macroscopic Properties in Lead Halide Perovskites"

The paper "Dynamic Nanodomains Dictate Macroscopic Properties in Lead Halide Perovskites" presents an in-depth exploration of the intricate relationship between nanoscale structural dynamics and macroscopic properties in lead halide perovskites, specifically focusing on hybrid organic-inorganic perovskite solar cells and X-ray detectors. The work employs a multi-modal methodology combining X-ray diffuse scattering, inelastic neutron spectroscopy, and advanced machine learning-assisted molecular dynamics (MD) simulations to uncover insights into these materials' dynamic nanodomains and their significant roles.

The authors highlight the presence of dynamic, lower-symmetry local nanodomains within higher-symmetry average phases of various perovskite compositions. The paper investigates how A-site cation selection, specifically methylammonium (MA) and formamidinium (FA), influences the density and nature of these nanodomains. MA is observed to create dense planar nanodomains characterized by out-of-phase octahedral tilts, whereas FA encourages sparser spherical nanodomains with in-phase tilting. These nanodomains are shown to have direct correlations to the diverse macroscopic optoelectronic and ferroelastic properties observed in different perovskite compositions.

Methodological Insights

1. Experimental Approaches: The paper employs X-ray diffuse scattering to explore the local structures in MAPbBr₃ and FAPbBr₃ single crystals. The scattering patterns demonstrate the presence of local spatial correlations within these materials, revealing variations between MAPbBr₃ and FAPbBr₃ in terms of shape and distribution of nanodomains.
2. Machine Learning-Assisted Molecular Dynamics Simulations: Large-scale MD simulations, aided by machine learning-derived force fields, complement the experimental observations by providing detailed insights into real-space dynamics and allowing precise modeling of local structural arrangements. These simulations align well with experimental results and help quantify features like nanodomain size and density.

Key Findings

• Dynamic Nanodomains: The paper illustrates that the optoelectronic and ferroelastic behaviors of lead halide perovskites are heavily influenced by the noncentrosymmetric dynamic nanodomains within them. These nanodomains, characterized by specific octahedral tilting patterns, can be tuned through A-site cation selection.
• Impact of A-Site Cations: The choice between MA and FA cations significantly affects the perovskites' local structural dynamics and, consequently, their macroscopic properties. FA-based perovskites show superior optoelectronic performance, attributed to their capability to form more advantageous local structures.

Implications and Future Directions

The findings of this research have substantial implications for the design and development of perovskite materials for photovoltaics and optoelectronics. By demonstrating the tunability of local structures through A-site cation selection, the paper opens pathways for engineering perovskites with specific macroscopic properties.

From a theoretical perspective, the work enriches the understanding of how local dynamic structural features relate to global material properties, highlighting a complex interplay that may extend beyond perovskites to other class of materials exhibiting similar structural characteristics.

Looking forward, the integration of machine learning models into the paper of material dynamics promises enhanced predictive capabilities and could drive advancements in material discovery and optimization. Additionally, further exploration of the ferroelastic properties may yield novel device applications leveraging the unique dynamic behaviors of these materials.