Investigation of electronic structures and interfacial chemistries of carrier injection layers in organic light-emitting devices via synchrotron radiation photoemission spectroscopy
Date Issued
2012
Date
2012
Author(s)
Hsu, Che-Chang
Abstract
In this thesis, synchrotron radiation photoemission was used to investigate the interfacial electronic structure at both electron and hole injection layers in organic light-emitting devices (OLEDs).
For hole injection layer, the molybdenum trioxide (MoO3) with high work function was employed. We found that upon annealing the MoO3 film the topotactic decomposition occurred to produce a large density of gap states, which was caused by increased the oxygen vacancies. These gap states not only provided the transition path for the carriers from the anode to the hole transporting layers (HTLs), but also induced a close alignment between the Fermi level and the HOMO state. In short, annealed MoO3 reduced the hole injection barrier, thereby enhancing the hole injection efficiency.
For electron injection layer, cesium fluoride (CsF) as electron injection layers was inserted between electron transporting materials (OXD-7) and aluminum. Cesium was found to attach the lone pairs of nitrogen, and interacted the oxadiazole moiety of OXD-7, thereby forming the Cs-OXD metal complex. The fluorine atoms bonded with the hydrogen of benzene moiety, giving rise to a weak ionic bond between cesium and fluorine. When aluminum was deposited onto cesium fluoride, the atoms lose electrons and became oxidized. The high polarity of aluminum ions attracted fluorine from the hydrogen of benzene moiety to form AlF3. The sequential chemical interaction among Al, F and Cs-OXD metal complex leaded to higher probability of electron transition and improved the electron injection efficiency.
Subjects
OLED
molybdenum trioxide
photoemission
synchrotron radiation
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
index.html
Size
23.27 KB
Format
HTML
Checksum
(MD5):ecf818b86bc6cfd923b1cf98cfa72b7f