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Published June 1998 | public
Journal Article

New Triarylamine-Containing Polymers as Hole Transport Materials in Organic Light-Emitting Diodes: Effect of Polymer Structure and Cross-Linking on Device Characteristics


A series of poly(norbornenes) with pendant triarylamine (TPA) groups has been synthesized by ring-opening metathesis polymerization and investigated as hole transport materials in organic two-layer light-emitting diodes (LEDs). Efficient device fabrication through spin casting of the hole transport layer (HTL) was possible, since the polymers exhibited excellent film formation properties. LEDs of the form ITO/poly(norbornene)-TPA/Alq_33/Mg (ITO) indium tin oxide, Alqq_3 = tris(8-quinolinato)aluminum) showed bright green emission with external quantum efficiencies of up to 0.77% (1.30 lm/W) for 20 nm thick HTL films. The length and polarity of the linker between the triarylamine functionality and the polymer backbone were varied systematically. The device performance was found to depend strongly on these structural differences. Substitution of ester groups by less polar ether functionalities greatly enhances external quantum efficiencies, lowers the operating voltage, and improves the stability of the device. Further improvement of the device characteristics is achieved by reducing the length of the alkyl linker. The HTL can be conveniently cross-linked by UV irradiation. Cross-linking was found to decrease device performance. A maximum external quantum efficiency of 0.37% was achieved for an Alq_3-LED with cross-linked HTL.

Additional Information

© 1998 American Chemical Society. Received January 21, 1998. Revised Manuscript Received March 19, 1998. We thank M. Weck, Dr. M. W. Wagaman, and Dr. B. R. Maughon for helpful discussions and M. Weck for contributing the norborn-2-ene-5-carbonyl chloride. Financial support was provided through Center for Advanced Multifunctional Nonlinear Optical Polymers and Molecular Assemblies (CAMP) by the Office of Naval Research.

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