Study On Organic Semiconductor Material

The study of low-dimensional Organic semiconductor materials has received much attention in recent years, especially due to the discovery of such effects as Electroluminescence phenomenon of poly (para-phenylene-vinylene) (PPV). The physics in low-dimensional systems presents new challenges both theoretically and experimentally. With the development of modern technology, it is now possible to produce Organic Optoelectronic Devices. Because Organic semiconductor materials maybe can be used in different areas, it has become one of the most important issues in modern physics.In the first chapter of my dissertation, the characteristics and the applications of organic semiconductor materials, and the research back ground, method and recent research achievements in organic semiconductor materials have been summarized. There after, PPV are selected as our research objects.In the second chapter, we introduce of a theoretical model used to studied organic semiconductor polymer --- SSH model and the expansion of the SSH model, and then a representative of the simple organic semiconductor polymer --polyacetylene is studied as an example , a kind of numerical calculation on the polymer is summarized.In the third chapter, we discuss the band structure of PPV with the rigid backbone background. Firstly, we study the electronic part under the Situation without electron-electron interaction (study lattice part with the classical approach), and then get the energies of the electronic levels and the wave function of each level in the ground state. Secondly, the electron-electron interaction is taken into account. And then we use an extended version of the SSH model which includes a description of the electron-electron interaction and calculate correlation energy and band structure of PPV. Finally, we discuss the influence of different length and dielectric constant of the mediumκon correlation energy and band structure of PPV. The results show that the correlation energyεcwill decrease as the length of the PPV chain increases; and dielectric constant of the mediumκhas a strong influence on the correlation energy, in the condition of same length of PPV chain,εcwill decrease asκincrease,meanwhile, it also show that band gap will decrease as the length of the PPV chain increases; And dielectric constant of the mediumκalso has a strong influence on the band gap, in the condition of same length of PPV chain; the band gap will decrease as κincrease.In the forth chapter, we studied the PPV system with consideration of the carbon atom vibration along the chain orientation. Due to the vibration of carbon atom, we obtained such a equilibrium equation that include energy minimum principle, by solving the Schr?dinger equation and the equilibrium equation self-consistently: the energies of the electronic levels and the wave function of each level in the ground state can be easily obtained. With the same method used by last chapter, we first discuss the situation without the electron-electron interaction and then discuss the situation with the electron-electron interaction. The result shows that different length and dielectric constant of the mediumκhas the same influence on correlation energy and band structure of PPV as the result we get in the third chapter. But the obtained band gap in this chapter is much more approached to the experiment values.In the last chapter, the main contents and conclusions of my dissertation have been summarized, and sequential research work is specified.