| Organic electroluminescence devices have attracted increasing attention in recent years because of their potential advantages in low-power, emissive, flexible, cost-competitive, flat panel. Some devices are available now, but their shortcomings of low efficiency, short life and unstable properties need solving urgently. Nowadays researchers in this field throw themselves into exploiting high electroluminescence efficiency, stable luminescence materials and carrier transport materials, improving device architecture and otherwise. In contrast to the rapid progresses made in the experimental front, systematic and comprehensive understanding of the various processes and the physics involved in the OLEDs is important.Based on the research results of other groups, the main results are listed as following:1. An analytical model to calculate the electroluminescence (EL) profiles at high electric field i n single 1 ayer structure was presented, t aking into account t he charge injection process at each electrode, disassociation and recombination of polaron-excitons. By simulation, the influence of disassociated distance on recombination efficiency and the influence of injection and recombination on EL efficiencies are thoroughly studied.2. Charge transport in a conjugated polymer thin film device with thermionic and tunneling charge-carrier injection was discussed. We consider that the polymer transport properties along the polymer are position dependent, with the charge-carrier mobility being smaller near the anode/polymer neighborhood. We also assume a charge density distribution that decreases exponentially from this interface. A parameter that indicates how deep material properties are altered is determined.3. Based on the current continuous equation, an analytical expression of carrier densities and current densities are presented. In the calculation, the boundary condition is determined by considering the injection current that can be easily measured in experiments. We discuss the distributions of electron density and electron current density; analyze the influences of electric field on the electron density, electron current density and recombination efficiency and the injection energy barrier on recombination efficiency.4. A simple analytic model for the total cell current in bilayer light-emitting diodes with ohmic contacts is presented. Results are in good agreement with bothexisting experimental data and numerical simulations. This model permits the semi quantitative analyses of the influence of the most important parameters on the EL and cell currents. In particular, dependence of cell recombination current d ensity on the material parameter Fh ,Fe and dependence of EL current and the electric field in HTL and ETL on the ratio of electron to hole mobilities and on the LED geometry are analyzed. It is found this model can reasonably elucidates the influence of some material parameters on the recombination current density and provides the methods to optimize the structure and to select suitable electroluminescent materials.5. Considering the formation and disassociation of polaron-excitons, an analytical model to calculate the width of recombination zone and the external quantum efficiency in single layer OLEDs was presented. The influences of applied bias and the thickness of the device on the width of recombination zone and the external quantum efficiency were thoroughly studied. The dependence of external quantum efficiency on the environmental temperature was also investigated. Based on the bilayer organic light-emitting diode with ohmic anode and injection limited cathode, the influences of thickness of hole transport layer and the energy b arrier o f OOI for holes on device recombination efficiency and width of recombination zone have been investigated, too.
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