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|Title: ||Studies of surfaces and interfaces in organic electronic devices|
|Other Titles: ||You ji dian zi qi jian zhong biao mian he jie mian de yan jiu|
|Authors: ||Liu, Zengtao ( 劉增濤)|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Organic electronics.|
Electronic apparatus and appliances.
|Notes: ||CityU Call Number: TK7870 .L58 2011|
xix, 144 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2011.
Includes bibliographical references.
|Abstract: ||There has been much progress in organic electronic devices in the past two decades due to their potential applications in optical and electronic fields. The performance of these devices, such as organic photovoltaic devices (OPVs), organic thin film transistors (OTFTs), and organic light-emitting diodes (OLEDs), depends critically on the properties of the electrode/organic and organic/organic interfaces.
In this work, X-ray photoemission spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) have been used to investigate the electronic and chemical structures at interfaces of different organic electronic devices. For OPV devices, we mainly focus on the donor/acceptor interfaces and discussed the relationship between the interfaces and the performance of OPV devices, especially the open circuit voltage. We found that the substrate, interface middle layer, and doping can all result in changes of the electronic structures at the donor/acceptor interface, which determines the performance of OPV devices.
For OTFTs, we studied pentacene/molybdenum oxide (MoO3) and copper phthalocyanine (CuPc)/MoO3 interfaces and discuss how the electronic structures of these interfaces determine performance of the corresponding OTFTs. Via analysis of the electronic structures of these interfaces, we found that the space charge region formed in organic layer leads to high conductivity and normally-on operation mode in the OTFTs. We also studied the electronic structure of the n-n isotype copper
hexadecafluorophthalocyanine (F16CuPc)/phthalocyanatotin (IV) dichloride (SnCl2Pc)
heterojunction by UPS and XPS. Due to charge transfer across the heterojunction,
energy level bendings were observed at the two organic layers. Formation of space
charge regions strongly determine performance of the transistor consisting of the
For OLEDs, we mainly studied the interface between carbon nanotube (CNT)
film as a novel anode material and N, N'-diphenyl-N, N'-bis(1-naphthyl)-(1,
1'-biphenyl)-4, 4'-diamine (NPB). Due to the lower work function of the CNT film
comparing to that of indium tin oxide (ITO), the height of the hole injection barrier is
high and leads to severe performance degradation. Reducing the height in a controlled
way is of scientific and technological importance for replacing ITO with the CNT film
as anode material. We found that a simple and widely-used UV-ozone treatment can
dramatically enhance the work function of CNT film. The height of hole injection
barrier at the interface between NPB and treated CNT film is remarkably lowered,
which will lead to improving the performance of devices. Then, we systematically
studied the effects of O2 and H2O exposures on the surfaces and interfaces of organic
materials in a control OLED by using UPS to understand the mechanisms of device
degradation. For different surfaces and interfaces, the effects of O2 and H2O exposure
were studied and discussed.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086300|
|Appears in Collections:||AP - Doctor of Philosophy |
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