| Organic spintronics plays a very important role in the research of OLED. In this thesis, we fabricated standard MEHPPV (poly(2-methoxy,5-(2'-ethylhexyloxy)-1,4-phenylene vinylene)) polymer devices with a Fe film or with Ferrocene dopant or with a organic spin-valve structure including Fe3O4/MEHPPV/Fe, by using spin-coating and conventional thermal evaporation in molecular vapor deposition system. We investigated the characteristics of the fabricated devices, and discussed the mechanisms for magnetic field dependence of the performance.Our experiment results show,1) Fe thin film can influence the devices performance positively. Tuned by magnetic field, the performance of the Fe thermal deposition with 1.0 nm nominal thickness is the most effective, the luminescence efficiency is 1.63 cd/A, maximally. One of the dominant mechanisms responsible for this performance is due to the interaction of free carriers with triplets within the devices through the mechanism proposed by Ern and Merrifield, which can cause the higher singlets proportion, and improve the amount of the free carriers within the devices and increase the current.2) Under the presence of the magnetic field of 25 mT, the luminescence efficiency of the device with ferrocene doping active layer reaches 3.61 cd/A maximally, and the EL enhancement is increased around 8%. We attribute the EL enhancement to the recombination of spin-polarized holes from ferrocene and non spin-polarized electrons from the A1 cathode in the doping devices. The magnetic field-dependent ratio of singlet induced by ferrocene should be due to singlet-triplet intersystem conversion upon the dispersion of the ferrocene.3) The performance of Fe3O4/MEHPPV/Fe shows spin-valve characteristic. We consider that magnetic field can polarize electrons and holes with anti-parallel configurations simultaneously, and then these polarized electrons and holes will form effective singlets in the polymers and recombine with photons. |
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