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关键词有机光伏材料 电子转移 单态裂解 非绝热动力学 Ml-mctdh
摘要有机光伏材料的能量转换过程,对实现可持续发展具有重要的意义。商业化制造的太阳能电池大多基于无机半导体材料(如硅),面临成本和污染等问题,因此急需发展新型的太阳能电池。近年来,基于有机光伏材料制造的有机太阳能电池获得了广泛关注。该类电池具有备选材料丰富,成本较低,容易加工,可以实现柔性器件制备等优点。但是有机太阳能电池存在光电转换效率较低等问题,目前还无法产业化。实验学家主要通过设计新材料、控制和优化制作条件等方法调控器件整体性能,提高光电转换效率。从理论层面上研究有机太阳能电池工作机理,对指导实验进行材料设计和器件制作,进而提高有机太阳能电池的光电转换效率具有重要意义。 第一部分工作,光诱导的激发态过程中,单态裂解现象是近年来在有机光伏材料中发现的一种光诱导现象。因其可以成倍的提高有机太阳能电池的光电转换效率,近年来得到了广泛的关注。但是单态裂解现象的机理一直存在争议。本文中我们使用多层多组态含时Hartree(ML-MCTDH)动力学方法研究了并五苯体系三态模型下的单态裂解现象。ML-MCTDH动力学结果表明该体系中单态裂解现象是由电荷转移态参与的超交换机制决定的。同时我们仔细研究了不同频率的振动自由度在单态裂解动力学中的作用,发现与电子跃迁共振的有限的几个振动自由度对动力学的贡献比较大,这一发现可以通过费米黄金规则的框架下通过超交换机理来理解。作为一种数值精确的动力学方法,ML-MCTDH研究不仅确定了单态裂解动力学的微观机理,同时还可以作为标准检测其他近似的动力学方法的准确性。 第二部分工作,光诱导的电子转移过程对有机光伏材料的光电转换起着至关重要的作用。我们对模型体系蒽C60给-受体间的电子转移过程从理论上进行了动力学研究。通过量化计算构建了全维度的电子转移模型哈密顿。量子动力学方法使用多组态含时Hartree(MCTDH)和多层多组态含时Hartree(ML-MCTDH)方法。ML-MCTDH允许我们对包含4个电子态246个振动自由度的全维电子转移模型哈密顿进行量子动力学研究。计算结果显示蒽C60给-受体间存在超快的电子转移过程。这部分的工作也表明ML-MCTDH是一种可以处理上百自由度的复杂系统的非常强大的量子动力学方法。 第三部分工作,1,4-diazapentalene heteroacenes是一种潜在的可用于有机场效应晶体管的n型半导体材料,因具有反芳香性而存在合成方面的困难。因此理论研究结构-稳定性关系可以为实验设计合成稳定的衍生物提供有益的指导。衍生物的主要设计思想包括:对中心母核的线性、非线性延拓,给电子、缺电子基团取代,给电子、缺电子杂环取代等。我们通过理论计算衍生物的核独立化学位移NICS(1)zz和重组能,理解其结构稳定性和电荷传输性质。研究发现线性融合芳香环可以增加衍生物的稳定性,缺电子杂环的取代也可以增强衍生物的稳定性。此外,线性融合芳香环以及缺电子杂环的取代也可以有效的降低电子输运的重组能。所以这两种方式可以为实验设计更稳定高效的有机场效应晶体管材料提供理论指导。 总之,本文通过使用近年来发展起来的全量子动力学方法多组态含时Hartree(MCTDH)以及多层多组态含时Hartree(ML-MCTDH)方法,对并五苯体系三态模型下的单态裂解现象以及蒽C60给-受体间电子转移过程进行了理论研究。通过动力学研究理解了单态裂解现象以及蒽C60给-受体间电子转移过程的微观机理。同时通过这部分动力学的工作也证实了ML-MCTDH是一种可以处理复杂系统的量子动力学计算的非常强大的方法。同时本文通过量化计算理论模拟了1,4-diazapentalene heteroacenes及其衍生物的稳定性和电荷传输性质,为指导实验合成稳定高效的有机场效应晶体管材料提供了理论指导。对场效应晶体管材料设计与筛选,提高能源利用率,促进产业发展都具有积极的意义。
其他摘要The solar energy conversion in organic photovoltaic materials, has important significance to realize the sustainable development. The commercial manufacturing solar cell is mostly based on inorganic semiconductor material (such as silicon), which is expensive and have pollution problems. Therefore it’s urgent to develop novel solar cell. In recent years, organic solar cell based on organic photovoltaic materials gained widespread attention for many reasons, such as the rich alternative materials, low cost, easy processing, and can achieve flexible device fabrication. But photoelectric conversion efficiency of organic solar cell is low, and still unable to industrialization. The experimental scientists design new materials, control the overall performance and optimization production conditions to improve the photoelectric conversion efficiency of organic solar cells. From the theoretical level to investigate the mechanism and guide the material design is very important for the solar energy conversion. Firstly, Singlet fission (SF) is supposed to potentially improve the efficiency of solar energy conversion in organic photovoltaic systems. The multilayer multiconfigurational time-dependent hartree (ML-MCTDH) method was employed to describe the singlet fission of the pentacene system with a three-state model. The ML-MCTDH result agrees well with the previous simulations using the Redfield theory, the hierarchical equation of motion (HEOM) and the symmetrical quasi-classical (SQC) theory. We carefully investigated the role of vibrational modes with different frequencies in singlet fission dynamics. Interestingly, we observed the important contribution of a few modes with frequency resonance to electronic transition. Such a finding can be understood by revisiting the super-exchange mechanism within the framework of Fermi’s golden rule. As a numerically exact method, ML-MCTDH not only provides an accurate description of the microscopy insight of the SF dynamics but also provides benchmark results to examine the performance of other approximated dynamical methods. Secondly, Electron transfer at the donor-acceptor heterojunctions plays a critical role in the photoinduced process during the solar energy conversion in organic photovoltaic materials. We theoretically investigate the electron transfer process in the anthracene/C60 donor-acceptor complex by using quantum dynamics calculations. The electron-transfer model Hamiltonian with full dimensionality was built by quantum-chemical calculations. The quantum dynamics calculations were performed using the multiconfigurational time-dependent Hartree theory (MCTDH) and multilayer (ML) MCTDH methods. The later approach (ML-MCTDH) allows us to conduct the comprehensive study on the quantum evolution of the full-dimensional electron-transfer model including 4 electronic states and 246 vibrational degrees of freedom. Our quantum dynamics calculations exhibit the ultrafast anthraceneC60 charge transfer process because of the strong coupling between excitonic and charge transfer states. This work demonstrates that the ML-MCTDH is a very powerful method to treat the quantum evolution of complex systems. Thirdly, 1,4-Diazapentalene heteroacenes are potential n-type semi-conductors which could be used as a new type of materials for organic field-effect transistors (OFETs), but their synthesis is still challenging due to their antiaromaticity. The study on their structure-stability relationship should provide useful guidance to the design of stable diazapentalenes. We examined the stability of several types of heteroacenes bearing the 1,4-diazapentalene core using NICS(1)zz calculations. The influence of the fusion pattern, the introduction of substituents, and the incorporation of other heterocycles on the antiaromaticity of the central 1,4-diazapentalene core was systematically studied. It was found that the linear fusion of aromatic rings to the antiaromatic core increases the stability of the heteroacene. The fusion of electron-poor heterocyclic rings also enhances the stability effectively, while the fusion of electron-rich heterocyclic rings destabilizes the system. In addition, the combination of the linear fusion pattern or introduction of electron-poor heterocyclic rings to the antiaromatic core also reduces the reorganization energy for electron transport, suggesting a way to achieve better n-type semiconductors. In summary, the singlet fission of the pentacene system with a three-state model and the electron transfer process in the anthracene/C60 donor-acceptor complex was investigated by the recently developed multiconfigurational time-dependent Hartree theory (MCTDH) and multilayer multiconfigurational time-dependent hartree (ML-MCTDH) method. The dynamics results give the accurate description of the microscopy insight of the SF dynamics and the ultrafast anthraceneC60 charge transfer process. At the same time this work also demonstrate that ML-MCTDH is a very powerful method to treat the quantum evolution of complex systems. At the same time, stability and charge transport properties of different molecular structures based on 1,4-diazapentalene heteroacenes were simulated, which provide a theoretical guide to synthesis stable and efficient OFET materials.
学位类型博士 ; 学位论文
GB/T 7714
郑杰. 有机光伏材料中光诱导过程的量子动力学研究[D]. 北京. 中国科学院大学,2016.
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