Nanotechnology

Atomic-level engineering of perovskite materials opens the way to new lasers and LEDs

Graphical summary. Credit: Matter (2024). DOI: 10.1016/j.matt.2024.09.010

Researchers have developed and demonstrated a technique that can process a class of materials called layered hybrid perovskites (LHPs) down to the atomic level. This determines exactly how the material converts electrical charge into light. This technology opens the door to engineering materials for use in next-generation printed LEDs and lasers, and is also promising for engineering other materials for use in photovoltaic devices.

The paper “Cationic Ligation Guides Quantum Well Formation in Layered Hybrid Perovskites” will be published in the journal Matter.

Perovskites are defined by their crystal structure and have desirable optical, electronic, and quantum properties. LHPs are composed of incredibly thin sheets of perovskite semiconductor material separated from each other by thin organic “spacer” layers.

LHPs can be arranged as thin films consisting of multiple sheets of perovskite and organic spacer layers. These materials are desirable because they can efficiently convert charge into light, which holds promise for use in next-generation LEDs, lasers, and photonic integrated circuits.

However, although LHPs have attracted the interest of the research community for many years, little was understood about how to process these materials to control their performance properties.

To understand what the researchers discovered, we need to start with quantum wells, which are sheets of semiconductor material sandwiched between spacer layers.

“We knew that a quantum well was formed within the LHP; it’s a layer,” said Aram Amashian, corresponding author of a paper on the study and a professor of materials science and engineering at North Carolina State University. say.

Additionally, it is important to understand the size distribution of quantum wells because energy flows from high-energy structures to low-energy structures at the molecular level.

“A quantum well two atoms thick has higher energy than a quantum well five atoms thick,” said study co-author Kenan Gundogdu, a professor of physics at North Carolina State University. say. “And for the energy to flow efficiently, you have to put quantum wells three to four atoms thick between quantum wells two to five atoms thick. , it must have a gentle gradient so that the energy flows in a cascade.

“However, people studying LHP continued to encounter an anomaly. The size distribution of quantum wells in LHP samples that can be detected by X-ray diffraction is similar to the size distribution of quantum wells that can be detected using optical spectroscopy. It will be different,” Amassian said. Say.

“For example, diffraction might tell us that a quantum well is two atoms thick, or that there is a three-dimensional bulk crystal,” Amassian says. “But if you use spectroscopy, you might find that there are quantum wells and 3D bulk phases that are two, three, or four atoms thick.

“So, the first question we had was, why do we see this fundamental disconnect between X-ray diffraction and optical spectroscopy? And our second question was, why do we see this fundamental disconnect between X-ray diffraction and optical spectroscopy? “How can we control the size and distribution of quantum wells?”

Through a series of experiments, researchers discovered the presence of nanoplatelets that play a key role in answering both questions.

“Nanoplatelets are individual sheets of perovskite material that form on the surface of the solution used to create LHP,” Amassian says. “We found that these nanoplatelets essentially act as templates for the layered material that forms beneath them. Therefore, if a nanoplatelet is two atoms thick, the underlying LHP is formed as a series of quantum wells two atoms thick.

“However, the nanoplatelets themselves are not stable like the rest of the LHP materials. Instead, the nanoplatelet thickness continues to grow, adding new layers of atoms over time. When the platelet is three atoms thick, three atomic layers are formed, and eventually the nanoplatelet grows so thick that it becomes a three-dimensional crystal.”

The discovery also resolves a long-standing anomaly as to why X-ray diffraction and optical spectroscopy give different results. Diffraction detects stacking of sheets and therefore does not detect nanoplatelets, whereas optical spectroscopy detects isolated sheets.

“What’s interesting is that we found that by fundamentally adjusting the size and distribution of the quantum wells in the LHP film, we could essentially stop the growth of nanoplatelets in a controlled way,” Amassian says. . “Also, by controlling the size and placement of the quantum wells, we can achieve superior energy cascades. This means that this material can efficiently and rapidly collect charge and energy for laser and LED applications. means.”

When researchers discovered that nanoplatelets play a very important role in the formation of the perovskite layer in LHP, they discovered that nanoplatelets can be used to create perovskites used to convert light into electricity. We decided to see if we could manipulate the structure and properties of other perovskite materials, such as in solar cells and other photovoltaic technologies.

“We found that nanoplatelets play a similar role in other perovskite materials, and that these materials can be manipulated to strengthen desired structures and improve solar power performance and stability.” said study co-author and ALCOA professor Milad Abolhasani. Chemical and Biomolecular Engineering at North Carolina State University.

The paper was co-authored by Kasra Darabi, Fazel Bateni, Tonghui Wang, Laine Taussig, and Nathan Woodward, all Ph.D. Graduate of North Carolina State University. Mihirsinh Chauhan, Boyu Guo, Jiantao Wang, Dovletgeldi Seyitliyev, Masoud Ghasemi, and Xiangbin Han are all postdoctoral researchers at North Carolina State University. Evgeny Danilov, director of the NC State Institute for Imaging Kinetics and Spectroscopy. Xiaotong Li, Assistant Professor of Chemistry, North Carolina State University. and Ruipeng Li of Brookhaven National Laboratory.

Further information: Kasra Darabi et al, cationic ligation-guided quantum well formation in layered hybrid perovskites, Matter (2024). DOI: 10.1016/j.matt.2024.09.010

Provided by North Carolina State University

Citation: Engineering perovskite materials at the atomic level opens the way to new lasers, LEDs (October 11, 2024) https://phys.org/news/2024-10-perovskite-materials-atomic-paves- Retrieved October 11, 2024 from lasers.html

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