UV light-emitting electrochemical cells based on an ionic 2,2′-bifluorene derivative

Hsiao Fan Chen, Chih Teng Liao, Ming Cheng Kuo, Yun Shiuan Yeh, Hai-Ching Su, Ken Tsung Wong*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


UV light-emitting electrochemical cells (LECs) were, for the first time, achieved by the ionic 2,2′-bifluorene derivative, 1, which was synthesized through covalent tethering of methylimidazolium moieties as pendent groups. LEC devices incorporating ionic bifluorene 1 without (Device I) and with (Device III) the presence of poly(methyl methacrylate) (PMMA) exhibited UV EL emissions centered at 388 and 386 nm with maximum external quantum efficiencies and power efficiencies of 1.06% and 7.44 mW W-1 for Device III and 0.15% and 1.06 mW W-1 for Device I, respectively. Transmission electron microscopy (TEM) images showed that 1 tends to form nanospheres due to amphiphilic nature. The presence of PMMA unified the size of nanospheres which greatly reduced the void area in films, suppressing the current leakage and enhancing the device efficiency. Furthermore, thicker thickness of the emissive layer of LECs increases the distance between carrier recombination zone and electrodes to avoid exciton quenching. Thus, a sevenfold increase in device efficiency was obtained in thicker UV LECs containing PMMA (Device III) as compared to thinner UV LECs based on neat films of 1 (Device I). The EL emissions in the UV region are successfully achieved by LECs based on 1, which are so far the shortest emission wavelength achieved in LECs.

Original languageEnglish
Pages (from-to)1765-1773
Number of pages9
JournalOrganic Electronics
Issue number10
StatePublished - 1 Jan 2012


  • Fluorene
  • Light-emitting electrochemical cells
  • Ultraviolet


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