新型有机半导体材料电荷传输性能及机理的理论研究

发布时间：2019-06-19 16:59

【摘要】：有机半导体材料因其特有的性质被广泛应用于有机场效应晶体管、有机光电二极管和有机光伏等器件中,各器件的工作性能都与有机半导体材料中载流子的迁移率有关。迁移率是一个重要的宏观物理参数,是表征材料光电性能的最基本参数。本论文将从第一性原理出发,基于全量子的电荷转移速率理论,利用蒙特卡罗方法得到扩散系数,并根据爱因斯坦公式得到载流子迁移率。该方法是考虑了核隧穿效应的跳跃模型,可以描述电荷传输的过程。我们进一步探讨了影响载流子迁移率的因素并深入理解电荷传输的机理。我们首先研究了分子的侧链取代基对有机半导体电荷传输性质的影响。重组能和转移积分是影响电荷转移速率两个重要的理论参数。取代基对转移积分的影响要远远大于对重组能的影响。基于同类共轭骨架,若仅从取代基对有机半导体材料堆积方式的影响来说,可以将取代基效应分为两种,一种是取代基的引入改变分子堆积方式,另一种是不改变分子堆积。我们先后考察了这两种取代基效应对电荷传输性质的影响。通过考察分子几何结构、电子结构性质、分子间堆积模式与电荷传输性能之间的关系,为设计新型高效传输材料提供理论依据。对于不改变分子堆积模式的取代基效应,我们分别考虑了?-?堆积和鱼骨状堆积两种堆积方式的烷基链体系。研究发现,迁移率随烷基链长度的变化趋势是有规律的。受堆积方式影响,即对于?-?堆积,迁移率随链长增长而减小,鱼骨状堆积则正相反。近来,给受体双组分双极性有机半导体材料因有望应用于互补电路和光电晶体管而受到广泛关注。在分子水平上,其电荷传输过程涉及直接的空间耦合和超交换耦合。对于只有直接的空间耦合的双组分双极性有机半导体材料,其电荷传输只与同组分的性质有关。我们研究发现,对于硫桥环轮烯/富勒烯混合晶体,分子间耦合主要发生在同类型分子间,并且富勒烯一条传输路径有多种耦合方式。而对于存在超交换耦合的材料,电子传输(空穴传输)与作为桥连接的给体分子(受体分子)的性质有关。我们用分子动力学模拟得到堆积构型的涨落,利用超交换作用得到分子间转移积分的涨落,并利用动态蒙特卡罗模拟得到迁移率,考察了动力学涨落对双组分双极性半导体材料硫桥环轮烯/四氰基对醌二甲烷电荷传输性质的影响。我们发现,核隧穿会导致“类能带”传输行为,并且动态无序会进一步降低迁移率。
[Abstract]:Organic semiconductor materials have been widely used in field effect transistors, organic photodiode and organic photovoltaic devices because of their unique properties. The working performance of each device is related to the carrier mobility in organic semiconductor materials. Mobility is an important macroscopic physical parameter and the most basic parameter to characterize the photoelectric properties of materials. In this paper, based on the first principle, based on the full quantum charge transfer rate theory, the diffusion coefficient is obtained by Monte Carlo method, and the carrier mobility is obtained according to Einstein's formula. This method is a jump model considering the nuclear tunneling effect, which can describe the process of charge transfer. We further discuss the factors affecting carrier mobility and deeply understand the mechanism of charge transfer. We first study the effect of the side chain substituents of the molecules on the charge transfer properties of organic semiconductors. Recombination energy and transfer integral are two important theoretical parameters affecting charge transfer rate. The influence of the substitution group on the transfer integral is much greater than that on the recombination energy. Based on the same kind of conjugated skeleton, if only from the effect of substitution group on the stacking mode of organic semiconductor materials, the substitution group effect can be divided into two kinds, one is the introduction of substitution group to change the molecular stacking mode, the other is not to change the molecular stacking mode. The effects of these two substituted radical effects on charge transfer properties have been investigated one after another. The relationship between molecular geometric structure, electronic structure properties, intermolecular stacking mode and charge transfer performance is investigated, which provides a theoretical basis for the design of new and efficient transport materials. For the substitution effect that does not change the molecular stacking mode, we consider it separately. The alkyl chain system of accumulation and fish bone accumulation. It is found that the mobility varies regularly with the length of alkyl chain. Affected by the way of stacking, that is, for Accumulation and mobility decreased with the increase of chain length, while fish bone accumulation was the opposite. Recently, two-component bipolar organic semiconductor materials for receptors have been widely concerned because they are expected to be used in complementary circuits and phototransistors. At the molecular level, the charge transfer process involves direct spatial coupling and hyperexchange coupling. For bipolar organic semiconductors with only direct spatial coupling, the charge transfer is only related to the properties of the same component. It is found that the intermolecular coupling mainly occurs between the same type of molecules for the mixed crystal of sulfur-bridged cyclic rotene / fullerene, and there are many coupling modes for the transmission path of fullerene. For materials with hyperexchange coupling, electron transport (hole transport) is related to the properties of donor molecules (receptor molecules) as bridge connections. The fluctuation of stacking configuration is obtained by molecular dynamics simulation, the fluctuation of intermolecular transfer integral is obtained by hyperexchange, and the mobility is obtained by dynamic Monte Carlo simulation. The effect of dynamic fluctuation on charge transfer properties of bipolar semiconductor material thio-bridged cyclic rotene / tetracyanyl group on quinodimethane is investigated. We find that nuclear tunneling will lead to "band-like" transmission behavior, and dynamic disorder will further reduce mobility.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.5

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