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Current-Induced Degradation in Polythiophene

Published online by Cambridge University Press:  11 February 2011

Velda Goldberg ,
Michael Kaplan ,
Leonard Soltzberg ,
Joseph Genevich ,
Emily Coombs ,
Erica Giacomozzi ,
Valarie Kwasnik ,
Samia Naeem ,
Eleana Pham  and
George Malliaras
Velda Goldberg
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Michael Kaplan
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Leonard Soltzberg
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Joseph Genevich
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Emily Coombs
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Erica Giacomozzi
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Valarie Kwasnik
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Samia Naeem
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
Eleana Pham
Affiliation:
Simmons College, Physics and Chemistry Departments, Boston, MA 02115
George Malliaras
Affiliation:
Materials Science Department, Cornell University, Ithaca, NY 14853
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Abstract

The three-year collaboration between Simmons College and the Cornell Center for Materials Research (CCMR) is focused on undergraduate student/faculty research in organic light emitting diodes (OLEDs). The physics of OLED devices is characterized by three major processes: charge injection, charge transfer, and light emission as a result of the electron-hole recombination. In the first year of the program our research has been related to the first two stages.

OLEDs based on small molecule as well as polymeric layers have been investigated. The devices were prepared using mostly aluminum (also nickel and iron) as electrodes and PC:TPD or polythiophene as the organic layer. Electrodes of about 20 nm were formed by vacuum evaporation, and organic layers of approximately 100–200 nm were spin-coated. The current-voltage characteristics, measured under forward and reverse bias up to 10 volts, demonstrate typical semiconductor S-shape behavior, and show variations dependent on aging, thickness of the polymer layer, and type and combination of electrodes.

The results presented here specifically track the degradation of devices using polythiophene sandwiched between aluminum electrodes. The I-V curves and successive current response as a function of time and under constant voltage drive are presented along with complementary mass spectra and UV-visible and infrared absorption spectra. These measurements along with preliminary computer modeling of HOMO and LUMO energies for a series of thiophene oligomers suggest a correlation between internal changes in the polymer and variations in the electrical characteristics of the devices.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 734: Symposia A/B – Defect-Mediated Phenomena in Ordered Polymers – Polymer/Metal Interfaces and Defect Mediated Phenomena in Ordered Polymers , 2002 , B9.4
Copyright
Copyright © Materials Research Society 2003

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References

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