| Organic electroluminescent devices (LEDs) have attracted increasing attention in recent years because of their potential advantages in low-power, emissive, flexible, cost-competitive, flat panel displays. Red, green, and blue light-emitting devices are readily available. In contrast to the rapid progress made in the experimental front, the basic understanding of the various processes (carrier injection, transport, recombination, device degradation, contact effects, doping effects etc.) in LEDs is still insufficient. Thus a systematic and comprehensive study of the physics involved in the carrier processes in LEDs is important and urgently needed.Although multilayer organic LEDs have an advantage in luminescent intensity and efficiency, because they exist some problems such as energy level matching between light-emitting layer and transport layer and complex fabricating technology etc. Single layer LEDs may be a better candidate for the practical application. Experimental results indicate that the luminescent intensity and efficiency is low and doping is an efficient means for enhancing efficiency and luminescent brightness for single layer organic light-emitting devices.The first part of this dissertation sums up the main research results on luminescence of the organic thin films. The main points are as following:1. The quantitative relations of the energy and charge transfer between substrate molecular and dopant in doped organic thin films were investigated. A model Hamiltonian was presented to describe the luminescence in thin films. It is found that it exists a correspondent relation between the amount of the transferred charge and the energy change due to doping, and the more the charge been transferred, the more the total energy decreased. According to the change of the fluorescence spectra and energy and charge transfer between PVK and perylene in doped PVK thin films, it is found that there are a correspondent relation between the position of fluorescence spectrum peak and the change of the system energy caused by doping and one between the fluorescence spectrum intensity and the amount of transferred charge due to doping. We deduce that the efficient energy transfer between PVK and perylene results from the charge transfer between them. The theoretical model can explainIVthe related experimental results.2. Formation and fission of polaron-excitons in organic light-emitting devices were investigated in detail. A theoretical model and a complete analytic function for polaron-excitons fission were presented. It is found that it exists two factors which influencing on fission of excitons. (1) Exciton fission might be caused by diffusion and by carrier hoping barrier in the absence of diffusion. (2) Carriers in the chain ends might be reflected or cause hoping between two chains. The influence of applied bias, temperature and dopant concentrations on recombination internal quantum efficiency were studied. This theoretical model could explain satisfactorily exciton direct fission and electroluminescence quenching at high applied electric field.3. According to current continuity equations and Poisson's equation, a complete analytic function for recombination probability density, current density and recombination efficiency was given. The results indicate that (1) Recombination density profile in single layer organic LEDs is found to be dictated primarily by the ratio of the carrier mobility and not by the relative injection ratio at anode and cathode. (2) The current-voltage characteristics show that fixing the cathode barrier and varying the anode barrier will result in the transition between space-charge-limited and contact-limited current flow. (3) The recombination efficiency is enhanced firstly and then decreased sharply and exists an optimum barrier value, with applied voltage increasing. These theoretical values are agreement with the related experimental data.4. Based on the physical processes of carrier transport and recombination, a model which describing carrier transport and...
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