Tunable molecular orientation and elevated thermal stability of vapor-deposited organic semiconductors

Journal Article · Mon Mar 23 00:00:00 EDT 2015 · Proceedings of the National Academy of Sciences of the United States of America

DOI:https://doi.org/10.1073/pnas.1421042112· OSTI ID:1235168

Dalal, Shakeel S.  ^[1]; Walters, Diane M. ^[1]; Lyubimov, Ivan ^[2]; de Pablo, Juan J. ^[2]; Ediger, M. D. ^[1]

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1. Department of Chemistry, University of Wisconsin–Madison, Madison, WI 53706, and
2. Institute for Molecular Engineering, University of Chicago, Chicago, IL 60637

Physical vapor deposition is commonly used to prepare organic glasses that serve as the active layers in light-emitting diodes, photovoltaics, and other devices. Recent work has shown that orienting the molecules in such organic semiconductors can significantly enhance device performance. In this paper, we apply a high-throughput characterization scheme to investigate the effect of the substrate temperature (T_substrate) on glasses of three organic molecules used as semiconductors. The optical and material properties are evaluated with spectroscopic ellipsometry. We find that molecular orientation in these glasses is continuously tunable and controlled by T_substrate/T_g, where T_g is the glass transition temperature. All three molecules can produce highly anisotropic glasses; the dependence of molecular orientation upon substrate temperature is remarkably similar and nearly independent of molecular length. All three compounds form “stable glasses” with high density and thermal stability, and have properties similar to stable glasses prepared from model glass formers. Simulations reproduce the experimental trends and explain molecular orientation in the deposited glasses in terms of the surface properties of the equilibrium liquid. Finally, by showing that organic semiconductors form stable glasses, these results provide an avenue for systematic performance optimization of active layers in organic electronics.

• Research Organization: Univ. of Wisconsin, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0002161
• OSTI ID: 1235168
• Alternate ID(s): OSTI ID: 1348214
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Vol. 112 Journal Issue: 14; ISSN 0027-8424
• Publisher: Proceedings of the National Academy of Sciences
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
glasses
organic semiconductors
molecular orientation
physical vapor deposition
high-throughput characterization