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Charge trapping and scattering by extrinsic gas dopants in tris(8-hydroxyquinoline) aluminum (Alq3)

Published online by Cambridge University Press:  17 March 2011

H.H. Fong  and
S.K. So
H.H. Fong
Affiliation:
Department of Physics and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong
S.K. So
Affiliation:
Department of Physics and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Kowloon Tong, Hong Kong Email address: [email protected]
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Abstract

The effects of various ambient gases (N2, O2, H2O) to the electron mobility of tris(8-hydroxyquinoline) aluminum, Alq3, were examined. For a clean Alq3, the electron transport is non-dispersive and essentially trap-free as revealed by optical time-of-flight measurements. At 295K, the electron mobility (μe) spans the range 0.2-1×10−6cm2V−1s−1 when the field varies from 0.4-0.9 MV cm−1. Exposing the sample to oxygen dosages in the range 1-100 Torr.s does not cause any noticeable changes in μe. The effect of oxygen on μe can be observed only at much higher oxygen dosages (>105 Torr.s). In contrast, exposing pristine Alq3 to moisture of same dosages causes a gradual reduction in μe by a factor of 4. It is proposed that oxygen diffuses into Alq3 during exposure and subsequently acts as charge scattering centers for externally injected free electrons. On the other hand, water induces charge traps at high dosages. Moisture control appears to be the most critical factor for the long-term operation of Alq3-based organic light-emitting diodes.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 814: Symposium I – Flexible Electronics 2004-Materials and Device Technology , 2004 , I10.18
Copyright
Copyright © Materials Research Society 2004

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