Interchain Electronic Hopping In Conjugated Polymers

Conjugated polymers have attracted many interests recently because of a unique set of properties: The electronic properties of metals and semiconductors and the processing advantages and mechanical properties of polymers such as flexibility. At present , numerous high-performance photoelectric devices fabricated from organic polymers have been made including light-emiting diodes, field efect transistors, photovoltaic cells,etc. Contrast to the traditional semiconductor, organic material has its unique- properties. First, most of the conjugated polymers have the qusi-one-dimensional structure due to the weak interaction force between the organic molecules. Second, owning to its soft properties, there are strong electron-phonon couplings in organic- systems. Especially, the additional charge (electrons or holes) or photoexcitation in conjugated polymers will induce latice deformation; on the contrary, the lattice defect will have the efect on the energy band structure of the organic system. So, it is generally. believed that these self-trapping excitations, such as solitons (only in traps -polyacetylene), polarons and bipolarons, are related to the charge carriers in conjugated polymers. These elementary excitations are of fundamental importance for transport properties photoluminescence of conjugated polymers system.In the past twenty years, the conjugated polymers have offered promise for use in applications, particularly in the area of optoelectronics where semiconducting luminescent polymers can be used to fabricate large area, flexible devices such as light-emitting diodes, displays, integrated circuits, solar cells, and plastic lasers. In 2004, Xiong et al. built a spin valve using the Alq3 as a spacer, where the Alq3 is sandwiched between layers of cobalt and half-metallic manganite La_0.7Sr_0.3MnO₃. Spin polarized injection and transport in organic semiconductor not only can broaden our understanding on the physical world of the organic materials but also can have a substantial impact on the applications of spintronics and bionomics. In recent years, it has been found that the photoexcited formations of the charged carriers and the exciton are tightly related. How to see clearly the relation and control the translation between them has been the focus in these years in order to improve the performance of the optoelectronic devices.Since 1970's, SSH Hamiltonian, the tight-binding semi-empirical calculation method that was found by Su, Schrieffer and Heeger has been demonstrated successfully for determining the electronic structures and optical properties in conjugated polymers. In the later years, Bishop, Sun and Xie et al have extended the SSH Hamiltonian to research the static and dynamic process of excitations. The further research in this field not only can broaden our understanding of the microcosmic physical world but also can have a substantial impact on the applications on organic polymer devicesIn this paper, in the framework of extended SSH model, we have studied some new properties of excitations. For intrachain photoexcitation,the output is exciton or intrachain oppositely charged polaron pair. For interchain photoexcitation,where an electron is excited from one chain to the other chain,is also investigated. the output is charge-transfer exciton, or intrechain oppositely charged polaron pair. So this photoexcitation is propitious to the photogeneration of charge carriers. In addition, the interchain coupling and on-site energy difference has a certain effect on the interchain charge transfer which makes the different quantum efficiency of charge carrier photogeneration in a solid-state sample from that in a solution.