Supercomputer Predicts Optical and Thermal Properties of Complex Hybrid Materials

Supercomputer Predicts Optical and Thermal Properties of Complex Hybrid Materials

The materials scientists at Duke University predicted by calculation the electrical and optical properties of semiconductors consisting of extended organic molecules sandwiched by inorganic structures.

These types of layered "organic-inorganic hybrid perovskites" – or HOIPs – are popular targets for light-based devices such as solar cells and light-emitting diodes (LEDs). The ability to create accurate models of these materials, atom by atom, will allow researchers to explore new material designs for next-generation devices.

"Ideally, we would like to be able to independently manipulate the organic and inorganic components of these types of materials and create semiconductors with predictable new properties," said David Mitzi, Professor of Mechanical Engineering and Materials Science at Simon Family in Duke . "This study shows that we are able to appear and explain the experimental properties of these materials through complex simulations of supercomputers, which is very exciting."

HOIPs are a promising class of materials because of the combined forces of their constituent organic and inorganic components. Organic materials have more desirable optical properties and may be flexible, but may be ineffective in carrying an electrical charge. Inorganic structures, on the other hand, are generally good at conducting electricity and offer more robust mechanical strength.

The combination of both can affect their individual properties while creating hybrid materials with the best of both worlds. Understanding the consequences of their interactions at the electronic and atomic levels is, however, at best difficult because the resulting crystals or films can be structurally complex. But since these HOIPs have their organic and inorganic components in well-ordered layers, their structures are a little easier to model and researchers are now starting to be successful in predicting their atomic behavior.

"The computer approach that we used has rarely been applied to structures of this size," said Volker Blum, an associate professor of mechanical engineering, materials science and chemistry at Duke. "We could not have done it even just 10 years ago. Even today, this work would not have been possible without access to one of the world's fastest supercomputers. "

This supercomputer, nicknamed Theta, is currently the 21st fastest in the world and resides at the Argonne National Laboratory. The group was able to save time thanks to Blum by associating with one of the twelve Theta Early Science projects, intended to pave the way for other applications on the system launched for the first time at the end of 2017. They are now co-researchers of a project of the prestigious "INCITE" award from the Ministry of Energy, entitled "Innovative and Innovative Impact of Computer Science on Theory and Innovation". 39, experience ", allowing them to continue their work.

In the new study, Chi Liu, a graduate student from Blum's lab; Yosuke Kanai, a theoretical colleague of the University of North Carolina – Chapel Hill; and Alvaro Vazquez-Mayagoitia, a scientist at Argonne National Laboratory, used Theta's computing power to model electronic states in a layered HOIP synthesized for the first time by Mitzi more than a decade ago. Although the electrical and optical properties of the material are well known, the physics behind their appearance has been the subject of much debate.

In a series of computer models, the team calculates the electronic states and locates the valence band and conduction band of the constituent materials of HOIP, organic bis (aminoethyl) quaterthiophene (AE4T) and inorganic lead bromide (PbBr4). . These properties dictate how electrons move through and between the two materials, which determines wavelengths and absorbed and emitted light energies, among other important properties such as conduction electric.

The results showed that the team calculations and the experimental observations agree, which proves that the calculations can accurately model the behaviors of the material.

Liu then went further by tweaking the materials – by varying the length of the organic molecular chain and substituting chlorine or bromine for iodine in the inorganic structure – and performing additional calculations. Experimentally, Mitzi and collaborator Wei You, a professor of chemistry and applied physics at the University of North Carolina – Chapel Hill, are working on the difficult task of synthesizing these variations to further test theoretical models of their colleagues.

This work is part of a larger initiative called HybriD3 project, which aims to discover and adjust new functional semiconductor materials. The collaborative effort includes a total of six teams of researchers. Professors Kenan Gundogdu and Franky So from the University of North Carolina and the University of North Carolina at Chapel Hill, as well as researchers from the Carolina State University of North, are working on the characterization of materials developed as part of the project and looking for prototypes of light emitting devices.

"By using the same type of calculation, we can now try to predict the properties of similar materials that do not exist yet," Mitzi said. "We can complete the components and, assuming the structure does not change drastically, provide promising targets to materials scientists."

This capability will enable scientists to more easily search for better materials for a wide range of applications. For this class of materials, this includes lighting and water purification.

Inorganic light sources are usually surrounded by diffusers to disperse and soften their intense, concentrated light, leading to inefficiencies. This class of layered HOIP makes it possible to make films that do it more naturally while wasting less light. For the purification of water, the material could be designed for efficient high energy emissions in the ultraviolet range, which can be used to kill bacteria.

"The more general goal of the project is to determine the material space in this class of materials in general, far beyond the organic thiophene observed in this study," Blum said. "The key point is that we have demonstrated that we can do these calculations with this proof of concept. Now, we must work to expand it.