CSD in action: principles to limit dynamic disorder in molecular semiconductors

Here we highlight a paper using the Cambridge Structural Database (CSD) and a novel approach to calculating dynamic disorder to identify the major characteristics of structures representing a low degree of dynamic disorder. This is part of our series highlighting examples of​​ the Cambridge Crystallographic Data Centre (CCDC) tools in action by scientists around the world.

Summary

In this work, authors from the University of Liverpool analyzed the dynamic disorder of approximately 5,000 small, organic molecules from the CSD to generate a list of key characteristics of structures that display a low degree of dynamic disorder. Such molecules present opportunities to create novel semiconductors for flexible, low-cost, and lightweight electronic devices. 

The team at Liverpool ran a novel dynamic disorder calculation on small molecules in the CSD. They then looked for correlations between the strength of dynamic disorder and molecular and crystal characteristics. They found that the strength of dynamic disorder is highly correlated with the gradient of the transfer integral. They also found that orientations of molecular pairs with fewer atoms in contact are more likely to yield low dynamic disorder, and that the presence of alkyl chains, the strength of the transfer integral, and the presence of heavy atoms also have an effect.

 

Why

Molecular semiconductors are held together by weak van der Waals forces that can be affected by the thermal motion of molecules at room temperature. That motion is known as dynamic disorder. A growing body of evidence suggests that the strength of dynamic disorder affects charge mobility and, therefore, semiconductor performance in electronic devices. Calculating dynamic disorder can prove a computationally expensive task, and the low energy associated with dynamic disorder makes it difficult to see experimentally. 

 

How

The team used a multi-scale quantum mechanics/molecular mechanics (QM/MM) methodology to speed up dynamic disorder calculations. They then used the structural data in the CSD to look for characteristics that correlate to low dynamic disorder, creating the first large database of computed dynamic disorder data to help with the design of new molecular semiconductors.

 

Read More

Read the full paper: "Strategies to reduce the dynamic disorder in molecular semiconductors," Mater. Horiz., 2020, 7, 2922-2928

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