Surreal illustration of layered crystals with glowing connections, symbolizing interlayer interactions in perovskites.

Beyond the Layers: Unveiling Non-Local Phononic Wonders in Perovskites

Elliot Brynn in Science & Nature August 2025 • 4 min read.

"Scientists explore the hidden influences of van der Waals forces on the structural and electronic behavior of Ruddlesden-Popper halide perovskites, potentially revolutionizing material design and applications."

For years, scientists have been captivated by layered materials, ranging from graphene to transition metal dichalcogenides, each possessing unique characteristics due to their structure. Layered materials generally have properties that are more or less independent of the number of layers due to the weak van der Waals (vdW) forces between the layers. Recent research is questioning this assumption, revealing that even these seemingly weak forces can dramatically alter material behavior. One such class of materials under intense scrutiny is the Ruddlesden-Popper (R-P) halide perovskites.

Perovskites, especially hybrid halide perovskites, have become materials science darlings because of their potential in solar cells, LEDs, and other optoelectronic devices. Unlike traditional layered materials, perovskites have a unique structure: semiconducting lead-halide layers interspersed with insulating organic layers. This creates a self-assembled multiple quantum well (MQW) structure, leading to fascinating properties, including the confinement of charge carriers and exceptionally high exciton binding energies. Understanding exactly how the layers interact within these perovskites is a key challenge.

New research is revealing the complexity of these interactions. Researchers are finding that van der Waals forces, along with the interplay of organic and inorganic components, lead to what are called “non-local phononic behaviors.” In other words, vibrations within the material aren't confined to individual layers; they extend across multiple layers, defying simple expectations. This discovery has major implications for how we understand and design these materials for future applications.

The Unexpected Power of Interlayer Forces

Surreal illustration of layered crystals with glowing connections, symbolizing interlayer interactions in perovskites.

A research team delved into the role of these subtle interlayer vdW forces in Ruddlesden-Popper perovskites, specifically focusing on high-quality epitaxial single-crystalline (C4H9NH3)2PbI4 flakes. Epitaxial growth ensures that the material's layers are highly ordered, which is crucial for precise measurements and understanding inherent properties. By creating flakes with carefully controlled dimensions, the scientists were able to observe how the material's behavior changed with thickness.

The team investigated two key properties: structural phase transitions (changes in the crystal structure with temperature) and electron-phonon coupling (how electrons interact with vibrations in the material). Both are critical for determining a material's optoelectronic performance. They found that both the interaction between the substrate and the perovskite and the interlayer vdW interactions played crucial roles in suppressing structural phase transitions. Interestingly, as the flakes became thinner (from ~100 nm to ~20 nm), the electron-phonon coupling strength decreased by about 30%. This suggests that reducing the material thickness diminishes the effectiveness of phonon confinement, challenging the conventional quantum well model applied to these materials.

Epitaxial Growth: Precise control over the growth of perovskite layers allowed for accurate measurements.
Structural Phase Transitions: Interlayer forces significantly impact crystal structure changes.
Electron-Phonon Coupling: Thinning the material alters how electrons interact with vibrations.
Challenging Conventional Models: Results suggest vdW perovskites are more complex than simple quantum wells.

These findings force a reconsideration of the conventional understanding of vdW perovskites as simple multiple quantum wells. The significant non-local phononic effects indicate that intralayer (within a layer) and interlayer (between layers) interactions aren't drastically different in magnitude. This means vibrations can propagate more freely than previously thought, influencing how electrons behave and ultimately impacting the material's performance. The study reveals that the interplay of these forces is far more intricate than initially appreciated and that long-range interlayer vibrations play a key role.

Implications for Future Materials Design

This research opens exciting new avenues for tailoring the properties of perovskite materials. By understanding the delicate balance of interlayer forces and their influence on vibrations, scientists can design materials with specific functionalities. This could lead to more efficient solar cells, improved LEDs, and novel electronic devices. The key lies in recognizing that these materials are not simply the sum of their individual layers; the interactions between layers are just as important, and provide unique opportunities for manipulation and control.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1021/acs.jpclett.8b02763, Alternate LINK

Title: Remote Phononic Effects In Epitaxial Ruddlesden–Popper Halide Perovskites

Subject: General Materials Science

Journal: The Journal of Physical Chemistry Letters

Publisher: American Chemical Society (ACS)

Authors: Zhizhong Chen, Yiping Wang, Xin Sun, Yu Xiang, Yang Hu, Jie Jiang, Jing Feng, Yi-Yang Sun, Xi Wang, Gwo-Ching Wang, Toh-Ming Lu, Hanwei Gao, Esther A. Wertz, Jian Shi

Published: 2018-11-06

Everything You Need To Know

What is the unique structure of Ruddlesden-Popper halide perovskites, and how does it contribute to their fascinating properties?

Ruddlesden-Popper halide perovskites are structured with semiconducting lead-halide layers alternating with insulating organic layers. This arrangement forms a self-assembled multiple quantum well (MQW) structure. This structure leads to unique properties such as the confinement of charge carriers and high exciton binding energies. The interplay between these layers, influenced by van der Waals forces, dictates the material's overall behavior and potential applications in optoelectronic devices. These interactions create non-local phononic behaviors, impacting material performance.

What are non-local phononic behaviors in Ruddlesden-Popper perovskites, and how could understanding them revolutionize material design?

Non-local phononic behaviors in Ruddlesden-Popper perovskites refer to the way vibrations extend across multiple layers, rather than being confined to individual layers. These behaviors arise from van der Waals forces and the interaction between organic and inorganic components. Understanding and controlling non-local phononic behaviors enables designing materials with specific functionalities, potentially leading to advancements in solar cells, LEDs, and novel electronic devices by manipulating interlayer interactions.

Why is epitaxial growth important in studying Ruddlesden-Popper perovskites, and what does it allow researchers to observe accurately?

Epitaxial growth is crucial because it allows for precise control over the arrangement of the perovskite layers. This level of control is essential for making accurate measurements and understanding the material's inherent properties. The high order achieved through epitaxial growth enables scientists to observe how material behavior changes with thickness, specifically concerning structural phase transitions and electron-phonon coupling. Deviations from precise epitaxial growth lead to inaccurate data, obscuring the true impact of interlayer van der Waals forces.

What are structural phase transitions in Ruddlesden-Popper perovskites, and how do interlayer forces affect these transitions?

Structural phase transitions in Ruddlesden-Popper perovskites are changes in the crystal structure of the material that occur with changes in temperature. The interplay of interlayer van der Waals forces and substrate interactions significantly influence these transitions. Understanding how to control structural phase transitions is vital because these transitions directly impact a material's optoelectronic performance. The ability to manipulate these transitions allows for the creation of materials with tailored functionalities and improved performance in applications like solar cells and LEDs.

How do the research findings challenge the conventional understanding of van der Waals perovskites as simple multiple quantum wells, and what implications does this have for future materials design?

The research findings challenge the conventional understanding of van der Waals perovskites as simple multiple quantum wells because they demonstrate that intralayer and interlayer interactions are not drastically different in magnitude. This implies that vibrations can propagate more freely than previously thought, influencing how electrons behave and impacting the material's overall performance. The significant non-local phononic effects reveal a more intricate interplay of forces than initially appreciated, emphasizing the importance of long-range interlayer vibrations. This necessitates a re-evaluation of design strategies for perovskite-based devices, moving beyond simple quantum well models to incorporate the complex dynamics of interlayer interactions.