Jee Yung Park, a PhD candidate and graduate research assistant in the Davidson School of Chemical Engineering, holds fluorescent crystals used in his work with multilayered perovskites.

By controlling the arrangement of multiple inorganic and organic layers within crystals using a novel technique, researchers at Purdue and Duke University have shown they can control the energy levels of electrons and holes (positive charge carriers) within a class of materials called perovskites. This tuning influences the materials’ optoelectronic properties and their ability to emit light of specific energies, demonstrated by their ability to function as a source of lasers.

Appearing online in the journal Nature Chemistry on Aug. 31, 2023, the research is the result of a close collaboration between several experimental and theoretical teams led by Letian Dou, Charles Davidson Associate Professor of Chemical Engineering at Purdue, who oversaw the overall effort to synthesize and characterize the layered perovskite structures.

“To me, growing nice crystals and resolving single-crystal structures of such complex organic-inorganic hybrid crystals are incredible achievements. These are the keys for a deeper understanding of their structure-property relationship. This work will guide the design of better solid-state laser materials in the future,” Dou said.

Perovskite materials are a class of compounds that have gained significant attention in the field of materials science due to their unique properties, particularly in the area of semiconductors. The materials, which are defined by their specific crystalline structure, can be used in applications like light-emitting diodes (LEDs), solar cells and lasers.

“Our work gets us one step closer to efficient lasing from these materials via careful design and characterization,” Dou said.

Jee Yung Park, a PhD student in Dou’s group, and Libai Huang, professor of physical chemistry in the College of Science, are co-authors on the paper, which focuses on refining the structural control of layered perovskite materials with organic semiconductor incorporation. While these types of perovskites have been made before with single layers of organic and inorganic components, the ability to precisely control the thickness of the inorganic component and, thus, adjust the properties of the material, has remained elusive for these more complex organic semiconductor-incorporated perovskites.

“By adding rigid organic semiconductor molecules, we make the soft hybrid crystals harder, and in this way, they emit light more efficiently,” Park said.

One important foundation of the computational work is a long-standing investment into the creation of computational simulation codes for materials properties.

“We’ve invested almost 20 years into being able to make these kinds of calculations in larger systems,” said Volker Blum, associate professor of mechanical engineering and materials science at Duke. “This study involved simulating structures including up to around 900 atoms with an advanced methodology, which requires powerful supercomputers that can handle some of the largest calculations on the planet.”

According to their findings, the organic components added to the inorganic layers affect the semiconductor properties, such as energy levels and light emission. By carefully controlling the arrangement of atoms and the number of layers in these structures, the researchers can tune the optical and electronic properties of the resulting material.

Their research also addresses challenges in synthesizing these materials, including the need to mix different components that may not readily dissolve in the same solvent, like trying to mix oil and salt into water. Achieving precise layering and alignment in larger structures becomes more complex.

“It’s like taking salt and olive oil and trying to mix it into water,” Blum explained. “One dissolves and the other does not. And if you try to use gasoline instead of water, you end up with the same problem. Our collaborators were able to find a way to get both into solution and dry into ordered crystals, and we were able to model those crystals to help explain how they function.”

Source: https://pratt.duke.edu/about/news/growing-triple-decker-hybrid-crystals-lasers