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Cathodic Interface Modification And Magnetic Effect Of Organic Electroluminescent Devices

Posted on:2012-05-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Y SunFull Text:PDF
GTID:1108330434971435Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
Organic Light-Emitting Devices (OLEDs) have attracted extensive attention since the breakthrough in this field was achieved in1987. A lot of researches lead to a rapid development in this domain and the progress has further expanded to other field of organic devices such as organic solar cell, organic field effect transistor and organic memory device. The thesis can be divided into two major parts:one is the modification effect of LiF buffer layer on different metal cathodes; the other is the research of the magnetic field effect of organic semiconductor. The concrete work is listed as follows:1. Electron injection enhancement effect of LiF buffer layer on the cathode made of gold (Au), the typical metal with high work function. Owing to the very high work function, gold is generally considered not suitable for the cathode material of OLEDs. The OLEDs with Au cathode always have bad performance because of poor electron injection. However in our work, it is found that the performance of Au cathode OLEDs can be efficiently improved by introducing a LiF buffer layer and with its optimal thickness can even be comparable with that of conventional Al cathode device. The relationship between the thickness of LiF layer and the performance improvement is investigated. Because of the inert chemical character of gold, chemical reaction mechanism can be excluded. Thus we consider tunneling plays the major role, which is significantly different from Al cathode devices and therefore enriches the study of the mechanism of LiF buffer layer. Other materials such as Al2O3and BCP are also used as buffer layers of Au cathode devices.2. Electron injection enhancement effect of LiF buffer layer on the other metal material cathodes. The matching relationships of Al, Ag, and Au with LiF buffer layer have been studied in existing research. In our further work, the matching of LiF buffer layer with copper (Cu) and iron (Fe) cathode is also studied. Through experiments we found out the optimal thickness of LiF buffer layer matching Cu and Fe cathode, separately. The situation of Cu cathode is very similar to that of Au cathode, while there is some difference in Fe cathode device. We try to give some qualitative explanation.3. Study of the magnetic field effect (MFE) of OLEDs with nonferromagnetic electrode. In the experiment, we studied the relation between MFE and current efficiency of device by adjusting the device structure and then studied the relation between organic magnetoresistance (OMAR) and exciton. We think that there is no direct corresponding relation between MFE and current efficiency of device. However, there is some close relationship between MFE and the presence and density of exciton. The influence of metal atom to the MFE of luminance of OLED has also been researched.
Keywords/Search Tags:OLED, modification of cathode interface, electron injection, LiF bufferlayer, tunneling model, Au cathode, magnetic effect
PDF Full Text Request
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