The authors would like to thank the National Science Council (NSC) of Taiwan (NSC96-2113-M-006-009-MY3) and the Asian Office of Aerospace Research and Development (AOARD-08-4076) for financially supporting this research. Dr. Pakhomov is on leave from Russian Academy of Sciences, Institute for Physics of Microstructures, N. Novgorod, Russia. Dr. Ruei-Tang Chen from Eternal Chemical Co., Ltd is highly appreciated for providing the HY-PPV polymer. The technical assistance from Center for Micro-NanoTechnology of National Cheng Kung University is also appreciated.
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Full Paper
Organic-Oxide Cathode Buffer Layer in Fabricating High-Performance Polymer Light-Emitting Diodes†
Article first published online: 22 SEP 2008
DOI: 10.1002/adfm.200800403
Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Additional Information
How to Cite
Lee, T.-H., Huang, J.-C.-A., Pakhomov, G. L., Guo, T.-F., Wen, T.-C., Huang, Y.-S., Tsou, C.-C., Chung, C.-T., Lin, Y.-C. and Hsu, Y.-J. (2008), Organic-Oxide Cathode Buffer Layer in Fabricating High-Performance Polymer Light-Emitting Diodes. Advanced Functional Materials, 18: 3036–3042. doi: 10.1002/adfm.200800403
- †
Publication History
- Issue published online: 6 OCT 2008
- Article first published online: 22 SEP 2008
- Manuscript Received: 21 MAR 2008
Funded by
- National Science Council (NSC) of Taiwan. Grant Number: NSC96-2113-M-006-009-MY3
- Asian Office of Aerospace Research and Development. Grant Number: AOARD-08-4076
- Abstract
- References
- Cited By
Keywords:
- electroluminescence;
- polymer Light-emitting diodes;
- cathodes;
- polymeric materials;
- hole transport
Graphical Abstract
The origin of ethylene-oxide functionalized cathode buffer layer in fabricating high-performance PLEDs is discussed. The reaction of PEGDE layer with thermally evaporated Al suppresses the diffusion of Al into the light-emissive polymer layer, potentially inhibiting oxidization and generation of metal-induced EL quenching sites near the recombination zone. The salt-free, neutral PEGDE interfacial layer can be easily integrated with manufacturing procedures.
Abstract
Spin-casting or thermal evaporation in vacuum of a salt-free, neutral, organic-oxide ultra-thin film as a buffer layer with an aluminum (Al) cathode has become an alternative approach for fabricating high-performance organic and polymer light-emitting diodes (O/PLEDs). [Guo et al., Appl. Phys. Lett. 2006, 88, 113501 and Appl. Phys. Lett. 2006, 89, 053507] The electroluminescence efficiency of phenyl-substituted poly(para-phenylene vinylene) copolymer-based PLEDs is 0.16 cd A−1 when Al is used as the device cathode, but is approximately two orders of magnitude higher, 14.53 cd A−1, when an organic oxide/Al composite cathode is used. The polymer/metal junction in PLEDs with and without depositing an ultra-thin organic oxide interlayer is studied by X-ray photoelectron spectroscopy. Experimental results indicate that the deposition of an Al electrode causes the oxidation at the surface of the light-emissive polymer layer. Introducing an organic-oxide cathode buffer layer suppresses the oxidation and the diffusion of the Al atoms into the functional polymer layer. The formation of a carbide-like (negative carbon) thin layer, which accompanies interfacial interactions, is critical to the injection of electrons through the Al cathode. The balanced charge injection is responsible for the substantially improved device performance. This process is specific to the organic oxide/Al interface, as revealed by a comparison with similar device configurations that have Ag as the electrode, in which no significant interaction in the interface is observed.