Transition metal oxides as a hole-injection layer for organic light-emitting devices
Date Issued
2010
Date
2010
Author(s)
Yeh, Cheng-Hung
Abstract
The mechanism of transition metal oxide, dirhenium heptoxide (Re2O7), rhenium trioxide (ReO3), molybdenum oxide (MoOx) and ruthenium dioxide (RuO2), used as interlayers in organic light-emitting devices (OLEDs) are investigated. The electronic structures and interfacial chemical reactions are investigated with ultraviolet and x-ray photoelectron spectroscopy.
First of all, the influence of evaporation temperatures on the electronic structures of MoOx films and the electrical properties of organic light emitting diodes are investigated. MoOx films evaporated at a high temperature and a high deposition rate are close to a stoichiometric phase, but become less effective when they are used as a hole injection layer. However, when MoOx is evaporated at a lower temperature and a slower rate, there are large amounts of defect-related states present in the forbidden gap, which make the films behave like a high work function conductor and an effective hole injection layer.
Second, the electronic structures of Re2O7 and ReO3 films in OLEDs are investigated. The gap states of Re2O7 interlayer due to the frailty of longer Re-O bond make the films behave as a better hole injection layer in OLEDs.
Finally, the operation voltages at a current density of 4 (mA/cm2) decrease from 7.9 V to 5.4 V , 5.4 V, 5.8V and 6 V for OLEDs with 5-nm-thick ReO3 ,Re2O7, RuO2 and MoOx as interlayers, respectively. The maximum luminance is 13,300 (cd/m2) for the device with RuO2, compared to 2,200 (cd/m2) for the device without HIL. The maximum luminance value increases about 600% in OLED using RuO2. However, the performance of the current efficiency is 5.1 (cd/A) for the OLED without an HIL (ITO/TMO/NPB/Alq3/LiF/Al) and 3.5 (cd/A) for a similar device employing ReO3 as the HIL. We also investigate the accumulation of charge carriers as interfacial charges or dipoles at the interfaces of OLEDs.
Subjects
transition metal oxide
dirhenium heptoxide
rhenium trioxide
molybdenum oxide
ruthenium dioxide
ultraviolet and x-ray photoelectron spectroscopy
organic light-emitting devices
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-R97941070-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):66d8976c6e9c59b74deab6ff3fbe9836