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Proceedings Paper

Carrier injection and bipolar transport in NPB for single-layer OLEDs
Author(s): S. C. Tse; K. K. Tsung; S. K. So
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Paper Abstract

We studied the carrier injection and transporting properties of N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)- 4,4'diamine (NPB), a common hole transporter for organic light-emitting diodes (OLEDs). NPB was found to possess significant electron mobility from time-of-flight (TOF) measurement. With bipolar transporting ability, NPB was used to fabricate single-layer devices with a configuration of ITO/ PEDOT:PSS/ NPB/ Ca/ Ag. PEDOT:PSS was demonstrated to form a quasi-Ohmic contact to NPB by admittance spectroscopy (AS) and dark-injection space-charge-limited current (DISCLC) measurements. From current-voltage (JV) characteristics, single-layer NPB devices exhibited a bulk-limited hole current in low-voltage region. Electron injection was clearly observed at a turn-on voltage of about 4V, which coincided with the luminance-voltage measurement. In order to confine the recombination zone, dye-doped NPB layer was inserted into single-layer devices. This intentional doping technique made a notable improvement in current efficiency. The mechanisms of the doped devices were also addressed.

Paper Details

Date Published: 16 October 2007
PDF: 11 pages
Proc. SPIE 6655, Organic Light Emitting Materials and Devices XI, 66551Q (16 October 2007); doi: 10.1117/12.733775
Show Author Affiliations
S. C. Tse, Hong Kong Baptist Univ. (Hong Kong China)
K. K. Tsung, Hong Kong Baptist Univ. (Hong Kong China)
S. K. So, Hong Kong Baptist Univ. (Hong Kong China)

Published in SPIE Proceedings Vol. 6655:
Organic Light Emitting Materials and Devices XI
Zakya H. Kafafi; Franky So, Editor(s)

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