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The Korean Infomation Display Society (한국정보디스플레이학회)
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Photoelectron Spectroscopy Studies of the Electronic Structures of Al/RbF and $Al/CaF_2$ Cathodes for $Alq_3$-based Organic Light-emitting Devices

  • Park, Yong-Sup (Nano-Surface Group, Korea Research Institute of Standards and Science) ;
  • Lee, Jou-Hahn (Nano-Surface Group, Korea Research Institute of Standards and Science)
  • Published : 2005.03.21
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Abstract

The electronic structures of Al/RbF/tris-(8-hydroxyquinoline)aluminium ($Alq_3$) and $Al/CaF_2/Alq_3$interfaces were investigated using x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For both systems, the UPS showed a significant valence band shift following the deposition of the thin fluoride layers on $Alq_3$. However, the formation of gap state in valence region and the extra peak N 1s core level spectra showed different trends, suggesting that the alkali fluoride and alkali-earth fluoride interlayer have different reaction mechanisms at the interface between Al cathode and $Alq_3$. In addition, the deposition of Al has considerably less effect on the valence band shift compared to the deposition of both RbF and $CaF_2$. These results suggest that the charge transfer across the interface and the resulting gap state formation may have lesser effect on the enhancement of organic light-emitting device performance than the observed valence band shift, which is thought to lower the electron injection barrier.

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