The Peculiar Magnetic Effect Of Organic Semiconductor

Since found that the magnetic effect of organic light-emitting diodes (OLEDs), the researchers on this strange magnetic effect to pay a large amount of research work, they found many strange new means of Organic Magneto-condutance, forthcoming (OMC) and Organic Magneto-Electroluminescence (OMEL). At300k, in additional magnetic field, the added value of forthcoming OMC or OMEL can be up to a few or even ten percent. Because of its special performance, which can be in organic magnetic sensor technology, information storage, handwriting input and novel-efficient display play a very important value. In recent years, the study by the research teams at home and abroad, while the study on the mechanism of organic magnetic theory has made progress, but organic magnetic contains many key issues still need to be solved. Such as:within the scope of the ultra small magnetic field based on Alq3magnetic conductance curve of organic leds are with larger magnetic field within the scope of meet the B2/(B||+BO)2; Positive and negative magnetic conductance mechanism under the control of non-equilibrium transport mechanism; How to produce lorentz linear and non lorentzian lines; Whether different metal electrode characteristics can affect organic leds magnetic effect, etc.This thesis focuses on the key issues for research, and analyzes the mechanism and application prospects of organic magnetic effect. The ultimate goal of all studies is to fully understand and master the mechanism of organic magnetic effect and the basic law, hoping to find a way that can carry on the effective regulation to the organic magnetic effect of means, that to develop electrical, optical, magnetic a body multifunctional semiconductor devices.This thesis mainly includes the following several parts:(1) Chapter one firstly introduces some of the organic semiconductor research works, and the research teams have made new progress in recent years; Second, Outlines the researching the importance of organic semiconductor devices magnetic effect, and the value of the application of organic field effect, etc.; Finally analyzes the organic light-emitting diode magnetic problem urgently to be solved. The second chapter mainly introduces the preparation methods of organic light-emitting diodes, method and experimental apparatus and steps required for the measurement data, etc.(2) The third chapter organic light-emitting diode (OLED) based on Alq3has been fabricated. The structure of devices is ITO/NPB/Alq3/LiF/Al. The magnetic field effects on current and electroluminescence were measured with constant voltage bias at different temperatures. Within the large range of magnetic field, the magnetoconductance curves follow the rules of B2/(|B|+B0)2. While in a very small range around zero-field, the measurement results exhibit a strange ultrasmall magnetic-field effect. Such an ultrasmall magnetic-field effect around zero-field can be explained by considering the tuning effect on the carrier’s spin due to the hyperfine interaction between the spin of carrier and the spin of nuclear in organic molecule.(3) The fourth chapter organic light-emitting diodes with structure of ITO/CuPc/NPB/Alq3/BCP(x)/Al were fabricated in this work. The thickness of BCP is40,80and120nm, respectively. The magnetic field effects on the conductance (magneto-conductance, MC) of these diodes were measured at temperature range from300to15K, respectively. Results show that the MC responses of all the three devices reveal a positive component under low magnetic field at all working temperatures. However, the MC effects under high magnetic field of the BCP(x)-inserted devices show a strong dependence on the temperature and device thickness. In particular, the MC of BCP (120nm) device shows a sign inversion as decreasing the temperature. However, this phenomenon can not be observed in the BCP (40,80nm) devices. Only negative component of MC is existed in the two devices at low temperatures. We suggest that the positive MC in low magnetic field is caused by hyperfine interaction. Moreover, the sign inversion of MC at high magnetic field is caused by the interaction between the triplet excition with long lifetime at low temperature and holes which are intercalated by the BCP inserted layer.(4) In this chapter, Organic light-emitting diodes with structure of ITO/CuPc/NPB/Alq3/metal cathode (Ca, Al, Cu) were fabricated in this work. The Ca, Al cathode with low melting point was grown by thermal evaporation deposition, and the Cu cathode with high melting point was fabricated by electron-beam deposition. The magnetic field effects on electroluminescence (magneto-electroluminescence, MEL) of these diodes were measured at temperature range from300to15K, respectively. Results show that the MEL responses of all these three devices present a fast rise in low magnetic field at room temperature. However, with further increasing the magnetic field, the MEL effects of Ca, Al electrodes devices increase slowly and become saturated gradually. This magnetic field dependence of MEL in the devices with Ca (or Al) electrode was found to be insensitive with the preparation of metal cathode. In contrast, the high field MEL effect of Cu (or Au) electrode device shows a slow decrease. Moreover, as decreasing the temperature, the high field MEL effect of Cu electrode device becomes more obvious. We suggest that the MEL effects in low and high magnetic field effect of Ca, Al electrodes are caused by the hyperfine mixing. The MEL in low magnetic field effect of Cu, Au cathodes is also caused by the hyperfine coupling. The declining of MEL in Cu (or Au) cathode based device at high magnetic field can be explained as follows:electronic injection is difficult for Cu cathode, so the e-h capture zone is close to the cathode interface. Moreover, the Cu (or Au) atoms deposited by electron-beam evaporation have much higher energy than that deposited by thermal evaporation, which cause the Cu (or Au) atoms penetrating into NPB layer. Then, Cu (or Au) atoms with strong spin-orbit coupling strength have an interaction with the e-h capture zone, which causes the MEL declining at high magnetic.