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Ultrafast Photoconductivity in Organic Semiconductors

Published online by Cambridge University Press:  01 February 2011

Oksana Ostroverkhova
Affiliation:
oksana@physics.orst.edu, Oregon State University, Physics, 301 Weniger Hall, Corvallis, OR, 97331, United States
David G. Cooke
Affiliation:
dcooke@phys.ualberta.ca, University of Alberta, Physics, Edmonton, T6G 2J1, Canada
Frank A. Hegmann
Affiliation:
hegmann@phys.ualberta.ca, University of Alberta, Physics, Edmonton, T6G 2J1, Canada
John E. Anthony
Affiliation:
anthony@uky.edu, University of Kentucky, Chemistry, Lexington, 40506, United States
Vitaly Podzorov
Affiliation:
podzorov@physics.rutgers.edu, Rutgers University, Piscataway, 08854, United States
Michael E. Gershenson
Affiliation:
gersh@physics.rutgers.edu, Rutgers University, Piscataway, 08854, United States
Oana D. Jurchescu
Affiliation:
jurchescu@chem.rug.nl, University of Groningen, Groningen, N/A, 9747, Netherlands
Thomas T.M. Palstra
Affiliation:
t.t.m.palstra@rug.nl, University of Groningen, Groningen, N/A, 9747, Netherlands
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Abstract

We present comprehensive study of ultrafast charge carrier dynamics in a variety of organic molecular crystals. In all samples, we observed sub-picosecond charge photogeneration and band-like transport, characterized by (i) an increase in charge carrier mobility as the temperature decreases in a wide temperature range of at least 20 K – 300 K and (ii) mobility anisotropy in the a-b plane of the crystals. The temperature dependence of the decay dynamics of the transient photoconductivity reveals the presence of shallow trapping sites in herring-bone-type-structured crystals (such as pentacene (Pc), tetracene (Tc), and rubrene (Rub)), while such traps are apparently absent in “brick-wall”-type crystals (such as functionalized pentacene (FPc)). We also report on the measurements of the charge carrier mobility anisotropy in the a-b plane of two types of FPc single crystals. Anisotropies of approximately 3.5 and 11.6 were obtained in the crystals characterized by crystal structures favoring two-dimensional and one-dimensional charge transport, respectively, consistent with the degree of π-overlap along different directions in the crystals.

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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References

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