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Published February 1999 | public
Journal Article

Organic Two-Layer Light-Emitting Diodes Based on High-T_g Hole-Transporting Polymers with Different Redox Potentials


A series of soluble arylamine-based hole-transporting polymers with glass transition temperatures in the range of 130−150 °C have been synthesized. The synthetic methodology allows facile substitution of the aryl groups on the amine with electron-withdrawing and electron-donating moieties, which permits tuning of the redox potential of the polymer. These polymers have been used as hole-transport layers (HTLs) in two-layer light-emitting diodes ITO/HTL/Alq/Mg [ITO = indium tin oxide, Alq = tris(8-quinolinato)aluminum]. The maximum external quantum efficiency of the device increases if the redox potential of the HTL is increased to facilitate reduction of the positive charge carriers at the HTL/Alq interface. A fluorinated hole-transport polymer with a relatively large redox potential (390 mV vs ferrocenium/ferrocene) yielded the device with the highest external quantum efficiency of 1.25% photons/e-. The device stability, however, follows the opposite trend. The device with the most electron-rich HTL exhibited the best performance after prolonged usage.

Additional Information

© 1999 American Chemical Society. Received September 8, 1998. Revised Manuscript Received November 13, 1998. Publication Date (Web): January 21, 1999. We thank Prof. Neal R. Armstrong, Dr. Stephen Barlow, Dr. S. Thayumanavan, and Prof. Ghassan E. Jabbour for very helpful discussions and Dr. Steven Barlow and Dr. S. Thayumanavan for providing samples of the molecular TPD derivatives. Financial support was received through the Center of Advanced Multifunctional Nonlinear Optical Polymers and Molecular Assemblies (CAMP) from the Office of Naval Research. NSF-AASERT student support through BMDO-AFOSR is gratefully acknowledged.

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