Organic-Oxide Cathode Buffer Layer in Fabricating High-Performance Polymer Light-Emitting Diodes

Authors

  • Tsung-Hsun Lee,

    1. Department of Physics, Center for Micro/Nano Science and Technology Institute of Innovations and Advanced Studies, National Cheng Kung University Tainan, Taiwan 701 (Republic of China)
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  • Jung-Chun-Andrew Huang,

    1. Department of Physics, Center for Micro/Nano Science and Technology Institute of Innovations and Advanced Studies, National Cheng Kung University Tainan, Taiwan 701 (Republic of China)
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  • Georgi L'vovich Pakhomov,

    1. Institute of Electro-Optical Science and Engineering Advanced Optoelectronic Technology Center, National Cheng Kung University Tainan, Taiwan 701 (Republic of China)
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  • Tzung-Fang Guo,

    Corresponding author
    1. Institute of Electro-Optical Science and Engineering Advanced Optoelectronic Technology Center, National Cheng Kung University Tainan, Taiwan 701 (Republic of China)
    • Institute of Electro-Optical Science and Engineering Advanced Optoelectronic Technology Center, National Cheng Kung University Tainan, Taiwan 701 (Republic of China).
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  • Ten-Chin Wen,

    1. Department of Chemical Engineering, National Cheng Kung University Tainan, Taiwan 701 (Republic of China)
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  • Yi-Shun Huang,

    1. Department of Chemical Engineering, National Cheng Kung University Tainan, Taiwan 701 (Republic of China)
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  • Chuan-Cheng Tsou,

    1. Chi Mei Optoelectronics Corporation, Tainan Science-Based Industrial Park Taiwan, 741, (Republic of China)
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  • Chia-Tin Chung,

    1. Chi Mei Optoelectronics Corporation, Tainan Science-Based Industrial Park Taiwan, 741, (Republic of China)
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  • Ying-Chang Lin,

    1. National Synchrotron Radiation Research Center Hsinchu, Taiwan 30076, (Republic of China)
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  • Yao-Jane Hsu

    1. National Synchrotron Radiation Research Center Hsinchu, Taiwan 30076, (Republic of China)
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  • 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.

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.

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