Observation of spontaneous orientation polarization in evaporated films of organic light-emitting diode materials

Kohei Osada, Kenichi Goushi, Hironori Kaji, Chihaya Adachi, Hisao Ishii, Yutaka Noguchi

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)


The molecular orientation in organic semiconductor films determines device performances. In particular, the spontaneous orientation of a permanent dipole moment (PDM) along the surface normal direction induces a polarization charge at the hetero-interfaces of stacked multilayer devices, and the interface charge dominates the charge accumulation and injection properties. Spontaneous orientation polarization (SOP) has been observed in the “randomly oriented” films of several organic semiconductor materials, and is potentially inherent in many common materials. Herein, we report that 11 additional molecules of organic light-emitting diode materials, including thermally activated delayed fluorescence emitters, and horizontally oriented emitters and electron transporters, exhibit SOP in their evaporated films. The experimental results clearly indicate that SOP frequently occurs in “horizontally oriented” films as well as “randomly oriented” films. The factors contributing to SOP formation are discussed in terms of the figure of merit per PDM. We found that strong intermolecular interactions tend to reduce the figure of merit. Moreover, we suggest the impact of SOP on device performances.

Original languageEnglish
Pages (from-to)313-317
Number of pages5
JournalOrganic Electronics
Publication statusPublished - Jul 2018

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Chemistry(all)
  • Condensed Matter Physics
  • Materials Chemistry
  • Electrical and Electronic Engineering


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