Theoretical Studies Of The Relationship Between Molecular Structure And Charge Carrier Transport Properties For Organic Optoelectronic Materials

Charge Carrier transfer property of organic optoelectronic material is an important factor affecting the performance of an organic semiconductor, and therefore it is crucial to study the effect of the structure of organic optoelectronic materials on carrier transport property for development and application of new organic photovoltaic materials. This thesis focuses on the mobility of the carriers of several types of organic optoelectronic materials with solid-state crystal structure and deals with the effects of structures(such as substituent, the size of theπconjugated molecular system and molecular stacking) on the transport properties. It can provide a theoretical basis for experimental design. We studied the impact of substituent groups on molecular and electron structure, calculated the reorganization energy, analyzed molecular transfer path and calculated the transfer integral of each path, and predicted the mobility of the solid state carriers. This thesis mainly covers the following parts:1 We researched electronic structure and crystal carrier transport properties of the cross typeπ-conjugated molecules DPDSB, CNDPDSB and DDBB. We mainly explored impact of three different kinds type terphenyl of substituents on the cross molecule for skeleton. The results show that, the hole reorganization energy are all less than that of an electron, which is beneficial to the hole transport.. Charge distribution of a molecule with different substituents is very different. The introduction of appropriate substituents can reach the two-dimensional molecular structure of conjugation, which is conductive to the space charge delocalization. Different substituents of molecules have quite different transfer paths. Because the effective overlap between the molecules is larger, the mobility of hole has increased by 10 times and 3 times for electron. For molecule DDBB, having a more delocalized charge distribution, its hole mobility is 30 times higher than that of DPDSB,100 times higher than that of electron.2 We researched molecular and electronic structure, reorganization energy and charge-transfer integral of symmetric substituted anthracene derivates, and using Einstein relation calculated the carrier mobility at room temperature. The results show that anthracene derivates has a high carrier mobility as the same as pentacene. Calculation value is consistent with the experiment results. Due to strong intermolecular interaction, the intermolecular stacking is denser, it is conductive to the carrier transport. But also it can be found by calculating that the introduction of appropriate substituents, the change from hole transfer to electronic transfer can be achieved. This is to provide for a theoretical basis for their applications. The introduction of the appropriate substutuents, in enhancing the stability of the materials, at the same time, is more conductive to the transfer of carrier. These studies can provide a theoretical basis for the practical application of three anthracene derivates.3 Heterocyclic aryl compounds containing "chalcogenophene" BSBS, DNTT, Ph-BSBS, C12BTBT and C12BSBS are researched, we studied the molecular and electronic structure, calculated the reorganization energy, transfer integral and carrier mobility of the crystal structure. The results show that after introduction of symmetrical substituents in the side chain of BSBS, the molecules steric hinderance increases, the reorganization of the molecules increases, the intermolecular hole transfer integral decreases, and the electrons transfer slightly increases, the introduction of substituents greatly enhances the solvency of compounds. BTBT as the base compound has a better charge transfer capacity than BSBS. furthermore, BTBT can reduce costs in the application, at the same time, can avoid toxicity and pollution caused by selenium. This provides theoretical basis for design of new materials. Introducing well conjugated groups in the matrix can greatly increase the performance of molecular conjugation, so molecules form a larger delocalizedπbond, and form a more dense molecular stacking, while reduce the molecular reorganization energy. So is more conducive to the effective intermolecular charge transfer. For DPh-BSBS, after the introducing of phenyl, its steric greatly increases. Although the introducing of phenyl can enhance the ability of conjugation, the steric hinderance has more effect on the transport of charge carrier. We calculated that the mobility at room temperature is less than without substituents or with alkyl, but is slightly enlarged for electronic mobility. It was found that the introducing of appropriate substituents, in enhancing the stability of the materials, at the same time, is more conductive to the transfer of carrier. The introduction of the substituent needs to consider both the conjugation and the steric hindrance effect.4 We researched the molecular and electronic structure, molecular reorganization energy, charge transfer integral of the asymmetric heterocyclic acene containing pyrrole and furan rings Ar-BFC(1.R=H,2.R=OC6H13,3.R=OC10H21), using Einstein relation we calculated the carrier mobility at room temperature. The results show that Ph-BFC is a preferable bipolar material。The mobility of hole at room temperature is 0.88 cm2/V·s, and is 0.53 cm2/V·s for that of electron. After introducing the alkoxy, the ability of hole transfer enchances for molecules 4-OC6H13-Ph-BFC and OC10H21-Ph-BFC, while it weakens for electronic transfer, for 4-OC10H21-Ph-BFCthe mobility of hole is 1.75 cm2/V·s, and is 0.10 cm2/V·s for that of electron at room temperature. So it is more conducive for hole transfer. Interaction of intermolecular non-parallel coplanar for heterocyclic acene and edge to face interaction of side benzene ring and common-plane heterocyclic acene are major factor effecting the hole transfer. Interaction of intermolecular non-parallel coplanar for heterocyclic acene is key factor for electronic transfer. So the interaction of intermolecular non-parallel coplanar for heterocyclic acene is the crucial factor for the transfer of carrier. This provides a new way of design high mobility carrier-transporting materials. This is also provides a theoretical basis for the molecules in organic field-effect transistors as the active layer of the potential application.