Efficient Electron Injection Mechanism in Organic Light-Emitting Diodes Using an Ultra Thin Layer of Low-Work-Function Metals

Takahito Oyamada, Chiharu Maeda, Hiroyuki Sasabe, Chihaya Adachi

Research output: Contribution to journalArticle

58 Citations (Scopus)

Abstract

To achieve efficient electron injection in organic light-emitting diodes, we examine ultra thin layers (0.50 nm) of the low-work-function metals, Cs (1.9eV), Rb (2.2eV), K (2.3eV), Na (2.4eV), Li (2.9eV), and Ca (2.9eV) capped with aluminum (Al) as a cathode layer. While all the alkali metals show a decrease of driving voltage compared with a single Al cathode, the Cs layer especially shows a significant decrease, and we obtain a high current density of 1.9 A/cm2 at an applied voltage of only 10V by using this layer. We demonstrate that efficient electron injection is achieved when we use a Cs layer with a thickness of less than 3 nm, although electron injection efficiency abruptly decreases when using a Cs layer thicker than 3 nm. From the Cs thickness dependence of current-voltage characteristics, we conclude that Cs atoms form an alloy layer with aluminum atoms at the organic/Al cathode interface, organic layer/Cs:Al/Al, that significantly enhances electron injection compared with that obtained from bulk Cs layers.

Original languageEnglish
Pages (from-to)L1535-L1538
JournalJapanese Journal of Applied Physics, Part 2: Letters
Volume42
Issue number12 B
DOIs
Publication statusPublished - Dec 15 2003
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physics and Astronomy (miscellaneous)
  • Physics and Astronomy(all)

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