Influence Of Exction Recombination Zone Changes On The Magnetic Field Effect In OLED

Current and electroluminescence (EL) in organic electroluminescence devices without any magnetic material could be changed under external magnetic field, which called MC and MEL respectively. These phenomenons, observed by Kalinowski et al. in2003, have been received widespread attention. With the development in this field, Nguyen et al. found that the value of MC and MEL can reach26%and57%respectively, which inspire researchers’enthusiasm again. This is because that the large MC and MEL value at room temperature provide some potential application on organic magnetic memory. However, the value of MC and MEL could be changed with device structure and measure conditions. In order to reveal its physical original, different physical mechanisms have been proposed.In this M.S. Dissertation, we focus on two factors on the change of OMFEs:one is the movement of exction recombination zone changing with temperature; the other is the thickness of exciton recombination zone. Therefore, our primary purpose in this thesis is exploring the mechanisms for the OMFEs.The main contents are described as follows:(1) In the first chapter we introduce research background of OLEDs (such as the development of LED and OLEDs). And then, the mechanisms for OMFEs was introduced. such as. triplet-triplet annihilation (TTA) model etc. In the second chapter. we present the experimental methnods used in this thesis.(2) Organic electroluminescence devices, with the structure of ITO/CuPc/NP B/Alq3(emitting green light)/Alq3:DCM(emitting red light)/LiF/Al(double emittin g layers device) and ITO/CuPc/NPB/Alq3/LiF/Al(single light-emitting layer referen ce device), have been fabricated in this paper. The magnetic field effects on elec troluminescence and current (MEL and MC) were studied under different tempera tures. The results show that the high field effect (B>50mT) of MEL in double emitting layers device decreases first, then turns to increase with decreasing tem perature. In contrast, the single light-emitting layer device increases monotonically, at the same injection currents. Moreover, the two spectral peaks at533nm and600nm in double emitting layers device coming from DCM and Alq3respectiv ely, show one falling and the other rising with decreasing temperature, which ind icates the exction recombination region shifting with changing temperature. The n onmonotonic changes in the high field effect of the MEL are discussed, and in t erms of the triplet-triplet interaction and carrier mobility change with the workin g temperature.(3) In this work we explore roles of the exciton recombination zone (RZ) on magnetic-field effects in tris-(8-hydroxyquinolinato) aluminum (Alq3) based orga nic light-emitting diodes by altering the thickness of Alq3. The magneto-electrolu minescence and magneto-conductance (MC) in these devices were investigated at various temperatures and bias voltages. It is found that the sign of MC changes from positive to negative, and then back to positive with the reduction of the t hickness of Alq3at50K. The phenomenon observed is ascribed to the change of the exciton density in the exciton RZ. Based on the mechanisms including th e hyperfine mixing, the triplet-charge interaction and interfacial dissociation or qu enching of excitons, the observed results were explained qualitatively...