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Light-Emitting Diodes Using Semiconducting Oligothiophenes

Published online by Cambridge University Press:  16 February 2011

K. Uchiyama ,
H. Akimichi ,
S. Hotta ,
H. Noge  and
H. Sakaki
K. Uchiyama
Affiliation:
Quantum Wave Project, ERATO, Research Development Corporation of Japan, 3–10–1 Higashimita, Tama-ku, Kawasaki 214, Japan
H. Akimichi
Affiliation:
Quantum Wave Project, ERATO, Research Development Corporation of Japan, 3–10–1 Higashimita, Tama-ku, Kawasaki 214, Japan
S. Hotta
Affiliation:
Quantum Wave Project, ERATO, Research Development Corporation of Japan, 3–10–1 Higashimita, Tama-ku, Kawasaki 214, Japan
H. Noge
Affiliation:
Quantum Wave Project, ERATO, Research Development Corporation of Japan, 3–10–1 Higashimita, Tama-ku, Kawasaki 214, Japan
H. Sakaki
Affiliation:
Quantum Wave Project, ERATO, Research Development Corporation of Japan, 3–10–1 Higashimita, Tama-ku, Kawasaki 214, Japan Research Center for Advanced Science and Technology, University of Tokyo, 4–6–1 Komaba, Meguro-ku, Tokyo 153, Japan
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Abstract

The light-emitting diodes (LEDs) using semiconducting oligothiophenes, dimethylquater-thiophene (DMQtT, tetramer), dimethylquinquethiophene (DMQqT, pentamer) and dimethyl-sexithiophene (DMSxT, hexamer), have been investigated. These oligomers were deposited on ITO-coated glass in ultra high vacuum and an aluminum electrode was subsequently vacuum-deposited on top of the oligomers. These structures have the diode configuration with Schottky barrier between the oligomers and aluminum.

The LED using DMSxT shows good rectifying feature with the rectifying ratio of 1500 at ±10V.Red-orange emission is clearly observed above 4V bias. In this LED, DMSxT acts not only as an emitting layer but also as a hole transport layer. We have also fabricated and studied alternate layered structures of DMSxT/DMQtT and DMSxT/DMQqT as the emitting layer. In these configurations, the carrier recombination can be modulated because both DMQtT and DMQqT have energy gaps wider than that of DMSxT.The quantum efficiencies (photons emitted per carriers injected) of the LEDs using DMSxT/DMQtT and DMSxT/DMQqT are about one hundred times and one thousand times larger than that of the LED solely based on DMSxT, respectively. These results indicate that the layered structures are advantageous in increasing quantum efficiency of the emission.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 328: Symposium Q – Electrical, Optical, and Magnetic Properties of Organic Solid State Materials , 1993 , 389
Copyright
Copyright © Materials Research Society 1994

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References

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