The Magneto-electroluminescence Caused By Various-combined Mechanisms In Organic Light Emitting Diodes

In recent years, the magnetic field effects in organic light emitting diodes (OLEDs) without any magnetic material has also aroused people’s attention. Researchers have proposed many theoretical model to explain the mechanism of organic magnetic effect. But with the deepening of research, people found that the magnetic effect of OLEDs is complex and changeable, and there is not a microscopic mechanism can explain all the experimental facts. Each mechanism can only partially explain the magnetic field effect in OLEDs, but can not explain some strange magnetic field effect very well. Therefore, to explore the mechanism of these complex magnetic field effect has become one of the focus of researchers.In this M.S. Dissertation, first we investigate the magneto-electroluminescence (MEL) and its influencing factors in OLEDs. We analys the MEL with the changing of the doping concentration、injected current density and temperature in the doped OLEDs. Then, we investigate the change of the MEL in doped OLEDs with the singlet exciton fission (STT) and triplet-triplet annihilation(TTA) process, trying to explore competition and micro differences between STT and TTA. The main contents in this Dissertation are follows:(1) First, this paper introduces the development course and current situation of the development of organic field effect; then the background of magnetic field effects based on the OLEDs and reseach progress at present were described and we provided some basis knowledge about convention OLEDs, such as the hyperfine interaction model, triplet-triplet exciton quenching model, singlet exciton fission model, etc. In the second chapter, we present the experimental methods in this thesis.(2) The Rubrene-doped organic light emitting diodes were fabricated by doping Rubrene, containing the singlet-triplet energy-resonant property (ES≈2ET), into phosphorescent-based host materials with different concentrations to investigate their magneto-electroluminescence (MEL). The results show that the MEL responses, including the low field component (B≤5 mT) and the high field component (5 mT≤B≤500 mT), change significantly with the doping concentration. These MEL curves could be attributed to the hyperfine interaction, singlet excition fission and triplet-triplet annihilation three-combined processes; the triplet excition has important effect on the luminescent intensity in OLEDs through changing the proportion of singlet exciton. In addition, the influence of temperature and injection current density on the MEL further supports our suggestion.(3) The doped OLEDs with structure of ITO/CuPc/NPB/Alq3:Rubrene/BCP/LiF/Al were fabricated by using co-evaporation technics to investigate their MEL with different Rubrene concentrations. The results show that the MEL responses change significantly with the doping concentration. Due to TTA and STT process existed together in the doped OLEDs,we argues that MEL curves could be attributed to the STT and TTA mechanisms coexist and compete; And with the decrease of the Rubrene concentration, the distance between Rubrene molecules increases, STT effect intensity is abate, whereas TTA effect is not affected by it, the competition and micro differences between STT and TTA is studied from the aspects of MEL. In addition, the influence of temperature and injection current density on the MEL further supports our suggestion.