The Magnetoconductance In Organic Optoelectronic Devices

Organic magnetoconductance was used to describe the changes of current in the organic optoelectronic devices with not magnetic materials under the external magnetic field. The OMC values of these devices can be up to a few or even ten percent under the influence of magnetic field with its magnitude of tens Milli-Tesla. Based on this characteristic, the OMC effects will play more important applications in information storage, sensor technology and handwriting input. Despite much progress in theoretical research has been made with gradually deepening efforts, there has much issue still unclear. For example, the original of the positive and negative OMC, the mechanism of the Lorentz and non-Lorentz line type, the influence of the aging treatment on the OMC effects.In this M.S. Dissertation, we focus on two issues including the original of the negative OMC and the influence of the degradation on the OMC effect, in particular the influence of the interaction between the carriers and triplet excitons. Based on the above investigation, the original of the OMC will be revealed and the application of the OMC will be explored. The main purpose of this paper is to find out the control method of OMC and develop a new-style multifunctional device with optical, electrical and magnetic properties synchronously.The main works in this Dissertation are listed as follows:(1) In the first and second charts, some basic knowledge of organic semiconductor was introduced. For example:π-conjugated structure in an organic molecule and "hopping transport" model in organic semiconductor, even the fundamental properties of OLEDs including carrier injection and the methods for enhancing the luminous efficiency. Then, a special focus will be on the three models of OMC effect. Last but not least, the necessary equipment for preparation and measurement in OLEDs was introduced.(2) The OLEDs with unbalanced transport properties was prepared utilizing BCP insert to the NPB and Alq3 layers. The device structure is ITO/CuPc/NPB/NPB: DCM/BCP/Alq3/LiF/Al. In order to compare, the device with balanced transport properties also been prepared, which structure is ITO/CuPc/NPB/Alq3/LiF/Al. The magnetic field effects on current (Organic magnetoconductance, OMC) were studied under different bias voltages and temperatures. Results show that the OMC of the BCP device contains two components, a positive low-field component and a negative high-field component. After our analysis, the mechanism based on the magnetic field modulated triplet-charge interaction is proposed to cause the high-field decrease. This research provides experimental evidence for the controversial issue in the OMC.(3) A hole-transport limited device with the structure of ITO/CuPc/NPB/BCP/ LiF/Al was prepared through utilizing BCP layer to replace the common electron transport material Alq3. Compared with the above BCP device, the hole-transport limited device will exclude the interference of Alq3. We aimed to investigate the interaction between the triplet excitons and the excessive holes in this chapter. The result shows a negative high-field component at low temperatures in the hole-transport limited device. Different with the last chapter, the decreasing degree in this device has much deeper; even changed its sign under the high current. This research also provides experimental evidence for the controversial issue in the original of the negative OMC(4) In this chapter, conventional OLEDs with structure of ITO/CuPc/NPB/Alq3/ LiF/Al were made. We investigate the influence of electric stress condition on the OMC effects. Results show that the magnitude of the OMC increases firstly and then gets smaller while its line shape unchanged as the device aging time enhanced. Possible explanations for the above effects were proposed based on the mechanism of the device aging treatment. It is suggested that the decrease in OMC is assigned to the degradation at the interface of Al/Alq3.