【作者】 李平；

【导师】 张厚玉；

【作者基本信息】 吉林大学 ， 物理化学， 2016， 硕士

【摘要】 有机光电材料具有来源广、成本低、易加工、柔韧性好和能大面积生产等优点而被广泛地应用于有机发光二极管、有机场效应晶体管和有机太阳能电池中。但与无机半导体材料相比,其载流子迁移率仍有待进一步提高。过去二十年人们一直致力于通过实验合成寻求高载流子迁移率的有机材料和优化器件结构,器件的电荷传输性能已经取得了显著的提高。同时,随着计算机技术的快速发展和量子化学方法的不断完善,理论计算已逐渐成为研究有机光电材料电荷传输性能及预测材料载流子迁移率的强有力工具。聚噻吩类有机光电材料已被大量报道应用于有机半导体器件中,但由于单键的旋转使其共轭程度降低,限制了其在实际器件中的应用。稠环聚噻吩材料分子具有刚性结构同时延伸了π共轭程度,因而具有较好的电荷传输性能和稳定性。稠环聚噻吩分子中的S原子具有较高的极性有利于促进给电子能力。存在于分子外围的距离较小的分子间S...S相互作用使分子紧密而有序地堆积,有利于进一步提高其电荷传输性质。因此,我们以稠环聚噻吩类材料为对象,对其电荷传输性质进行研究。本论文基于量子化学基本理论及方法,我们计算了分子重组能、前线分子轨道、电离能及电子亲合势、芳香性、重叠积分及分子轨道间相互作用,并预测了材料的载流子迁移率,从而从微观角度解释微小的结构变化导致传输性能显著不同的原因,进而建立结构与性能间的关系,以期为实验上设计、合成具有高电荷传输性能的光电功能材料提供理论依据和指导。本论文选取稠环聚噻吩类材料为研究体系,对其电子结构及电荷传输性质进行深入研究。主要内容包括以下两个部分:第一部分:研究了结构对称性和连接模式对并噻吩二聚体电子结构及电荷传输性质的影响。我们对并噻吩二聚体分子的几何结构、重组能、电离能及电子亲合势、分子芳香性、前线分子轨道及载流子迁移率作了深入分析,来探究结构对称性和连接模式对电荷传输性质的影响。理论计算结果表明:相比于单键连接的二聚体,双键连接的二聚体由于延伸的π共轭使π-π堆叠轨道相互作用较强;分子对称性影响分子轨道电子密度分布,进一步决定其分子取向及分子间排列方式;高对称性的分子可以有效促进分子的有序排列从而提高电荷传输能力。因此,高对称性乙烯连接的二聚体是一类潜在的具有高电荷传输能力的半导体材料。我们的计算结果为设计高载流子迁移率的有机半导体材料提供了新的启示。第二部分:研究了硫氧化对聚噻吩及其衍生物电子结构及电荷传输性质的影响。我们通过对比分析聚噻吩及其衍生物和对应的氧化物的几何结构、重组能、电离能及电子亲合势、分子芳香性、前线分子轨道、晶体堆叠方式及电荷传输本质,来探究硫氧化的位置和程度对电子结构及分子排列方式的影响以及对电荷传输本质的影响。理论计算结果表明:硫氧化程度越大,使分子重组能越小,有利于电荷传输;硫氧化可以使分子的电子亲合势更负,从而降低电子注入能垒,增加氧化物阴离子在环境中的稳定性;同时有效减小分子芳香性及促进分子π-π堆积;说明硫氧化确实对分子电子结构及排列方式产生较大的影响。更重要的是,硫氧化是一种有效的途径可以将p-型半导体材料转换为双极型或n-型半导体材料。更多还原

【Abstract】 Organic optoelectronic materials have been widely used in organic light-emitting diodes(OLEDs), organic field-effect transistors(OFETs) and organic photovoltaic cells(OPCs) due to their advantages such as abundant sources, low cost, easy fabrication,good flexibility and large-area production. However, the mobilities of organic materials need to be improved in comparison to those of inorganic materials. Over the past two decades, researchers are focusing on designing new materials with high carrier mobility and optimizing the device structures experimentally, so far the device performance has been significantly improved. Correspondingly, with the rapid development of computer technology and the updating of quantum chemical methods, theoretical calculation is becoming a powerful tool to study the charge transport properties of organic materials and predict their carrier mobilities.Oligothiophene-based organic optoelectronic materials have been extensively reported and applied in organic semiconductors, but low conjugation because of the torsion of single bonds limit their application in practical devices. Fused oligothiophenes(thienoacenes) possess the advantages of rigid planarity and extended conjugation, thus leading to improved charge transporting properties and chemical stability. The sulfur atoms in thienoacenes have high polarizability and thus facilitate electron-donating properties. Multiple short intermolecular S...S contacts originating from the sulfur atoms at the molecular periphery can make the molecules densely packed in the solid state, resulting in the enhanced charge transport properties. Herein, we study the charge transport properties based on thienoacenes materias.In this dissertation, based on quantum chemistry theory and method, we explore the molecular reorganization energy, frontier orbitals, ionization potential and electron affinity, aromaticity, transfer integral and orbital interaction, and carrier mobility, aiming to explain why a structural change leads to significant effects on the charge transport properties at a microscopic level and establish the structure-property relationship. We hope our work could shed light on designing new organic optoelectronic materials and improve the performance of electronic devices experimentally. Here, we choose two typical systems based on thienoacenes and investigate their charge transport properties. Our work mainly includes two parts as follows:Part 1: The effect of structural symmetry and linking mode on the electronic and charge transport properties of dimers of dithienothiophenes were investigated by using density functional theory(DFT). To gain a better understanding of the effects of the structural symmetry and linking mode on the dimers, the geometrical structures, molecular reorganization energies, molecular ionization potentials(IPs) and electron affinities(EAs), molecular aromaticities, frontier molecular orbitals, as well as charge mobilities are analyzed for the investigated dimers of dithienothiophenes. The calculated results show that the vinylene-linked dimers have advantages over the directly single-bond linked dimers because of the large extent of π conjugation and thus enhanced π–π stacking interactions in their crystal structures. The molecular symmetry could affect the electron density distributions in the molecules, and further determine the molecular orientations and intermolecular arrangements. High molecular symmetry could facilitate the molecular packing in order, thus enhancing the charge transport. Therefore,the highly symmetrical vinylene-bridged dimers could be promising candidates for transistor applications. Our calculated results shed light on the molecular design of high performance organic optoelectronic materials.Part 2: The effects of sulfur oxidation on the electronic and charge transport properties of fused oligothiophene derivatives were studied in this part. Taking aim at the effects of oxidized location and extent on the modulation of electronic structures and charge transport properties of oligothiophenes, the geometrical structures, molecular reorganization energies, molecular ionization potentials(IPs) and electron affinities(EAs), molecular aromaticities, frontier molecular orbitals, as well as charge mobilities of oligothiophenes and corresponding S, S-dioxides are investigated through comparative analysis. The calculated results show that increasing the extent of oxidation will decrease the reorganization energy, which is favorable for charge transport; the introduction of sulfone group makes the EAs of S,S-dioxides more negative, thus lower the energy barrier for electron injection and improve the stability of their anions; The oxidation decrease the molecular aromaticities and facilitate the π-π packing. The calculated results would hint us that chemical oxidation of the sulfur atoms to S,S-dioxides is an effective strategy to modulate the electronic and charge transport properties of fused oligothiophene. It is also demonstrated that such oxidation of thiophene could be a potential approach to transform p-type thiophene-based semiconductor to ambipolar or n-type OFET materials.更多还原