Thermal vibrations and the dynamic disorder they create can detrimentally affect the transport properties of van der Waals bonded molecular semiconductors. The low-energy nature of these vibrations makes it difficult to access them experimentally, which is why we still lack clear molecular design rules to control and reduce dynamic disorder. In this study we discuss the promising organic semiconductors rubrene, 2,7-dioctylbenzothieno[3,2-b]benzothio-phene and 2,9-di-decyl-dinaphtho-[2,3-b:20,30-f]-thieno-[3,2-b]-thiophene in terms of an exceptionally low degree of dynamic disorder. In particular, we analyse diffuse scattering in transmission electron microscopy, to show that small molecules that have their side chains attached along the long axis of their conjugated core are better encapsulated in their crystal structure, which helps reduce large-amplitude thermal motions. Our work provides a general strategy for the design of new classes of very high mobility organic semiconductors with a low degree of dynamic disorder.
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S.I. acknowledges funding from the EPSRC, the Winton Programme for the Physics of Sustainability and the Cambridge Home and EU scholarship scheme (CHESS). A.E. acknowledges the Seventh Framework Programme of the European Commission: ESTEEM2 (contract number 312483) as well as the Royal Society. G.S. acknowledges postdoctoral fellowship support from the Wiener-Anspach Foundation.
Additional data related to this publication is available at the University of Cambridge data repository (https://www.repository.cam.ac.uk/handle/1810/253572).
Illig, Steffen; Eggeman, Alexander S.; Troisi, Alessandro; Jiang, Lang; Warwick, Chris; Nikolka, Mark; Schweicher, Guillaume; Yeates, Stephen G.; Henri Geerts, Yves; Anthony, John E.; and Sirringhaus, Henning, "Reducing Dynamic Disorder in Small-Molecule Organic Semiconductors by Suppressing Large-Amplitude Thermal Motions" (2016). Chemistry Faculty Publications. 81.