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Dopant Pairing in a Molecular Semiconductor

Published online by Cambridge University Press:  01 February 2011

Howard M. Branz  and
Brian A. Gregg
Howard M. Branz
Affiliation:
National Renewable Energy Laboratory Golden, CO 80401 U.S.A.
Brian A. Gregg
Affiliation:
National Renewable Energy Laboratory Golden, CO 80401 U.S.A.
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Abstract

Recent doping experiments in n-type perylene diimide (PPEEB) semiconducting thin films showed an unexpected quadratic dependence of electrical conductivity upon dopant molecule concentration. We propose that singly-ionized dopant pairs outnumber ionized unpaired dopants and dominate conductivity. Random association into dopant pairs during spin coating then explains the quadratic dependence. Classical calculations confirm that dopant pairing reduces the binding energy of the easiest-to-ionize electron. Our model agrees with the measured conductivity activation energy and magnitude, assuming typical electron mobility in the crystal. The random distribution of dopants implies their distribution cannot equilibrate during the spincoating process.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 725: Symposium P – Organic and Polymeric Materials and Devices-Optical, Electrical, and Optoelectronic Properties , 2002 , P4.2
Copyright
Copyright © Materials Research Society 2002

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