Tuning The Magnetic Field Effect In Organic Light Emitting Diodes

Since the magnetic field effects (MFEs) on luminescence and conductance were found in nonmagnetic organic semiconducting materials and devices, which have attracted tremendous scientific research interest. Magneto-electroluminescence (MEL) and magneto-condutance (MC), the relative changes of electroluminescence and conductance when an external magnetic field was applied, have been powerful tools to reveal the excited processes occurring in organic optoelectronic devices. To realize the application of OLEDs, tuning the MEL and signal by changing the internal microscopic excited process is promising for realizing the practical application of controllable MFEs in organic devices. Previously, Chen had investigated the variation of MEL after adjusting the density of triplet excitons, and Hu also tune the MEL and MC by mixing the molecules with different spin-orbit coupling strengths. However, the ways of tuning MEL and MC are still not enough, and seeking more practical methods is still a valuable work for development of integrated magnetic-optic-electronic multifunctional devices.In this work, we focus on the ways of tuning MEL and MC. Tuning MEL is by the way of controlling the competition between singlet exciton fission (SF) and triplet exciton fusion (TF), which play an important role in luminescence in organic light emitting diodes (OLEDs). And we tuned MC mainly by changing the different metal cathodes, relying on the triplet-charge annihilation mechanism. Changing the measured temperature and injection current can also tune the MC.The main work in this Dissertation consists of several sections below:(1)In the first charted, some basic knowledge and current situation of OLEDs is introduced and the development history of organic magnetic field effects and its theoretical models, for example, singlet exciton fission, triplet exciton fusion, triplet-charge annihilation, intersystem crossing and so on. And we described the properties of OMFE in the Alq3 based OLEDs and rubrene based OLEDs, respectively. And the second charted mainly represents the fabrication and measure methods of OLED, especially recommending several different depositing metal methods.(2)The third charted mainly introduces the ways of tuning MEL. The OLEDs with structure of ITO/CuPc/NPB/rubrene:doped DCJTB/BCP/LiF/A1 were fabricated, and different doping concentration was used to control the competition between SF and TF. The result shows that TF process strengthened with the increasing concentration. The curves of MEL changes from the curve of SF to TF, and the magnitude at ±500 mT declined gradually. From the spectrum, we can see that the peak of spectrum changed from rubrene to DCJTB. At different temperature, the MEL also can be tuned, with the decreasing temperature, TF strengthened, the curves and the magnitude of MEL changed.(3)The fourth charted introduces the ways of tuning MC. And we fabricated the OLEDs with different metal cathodes, the structure is ITO/CuPc/NPB/rubrene/ BCP/metal cathodes, the metal cathodes include Al, Au, Ca. At room temperature, the MC were measured. The result indicates that the MC of OLED with A1 shows different curves compared with the OLEDs with Au and Ca. Different temperature and injection current can also tune the MC.