Application of the dielectric-dependent screened exchange potential approach to organic photocell materials
Application of the dielectric-dependent screened exchange potential approach to organic photocell materials
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介电相关屏蔽交换电位方法在有机光电池材料中的应用
DOI：
10.1039/c6cp04863c
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
T. Shimazaki and T. Nakajima
中科院分区：
文献类型：
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作者：
T. Shimazaki;K. Kitaura;D. G. Fedorov;and T. Nakajima;M. Nakata and T. Shimazaki;T. Shimazaki and T. Nakajima;Emiko Okamura;T. Shimazaki and T. Nakajima
本文讨论了有机分子和光电池材料的介电相关屏蔽交换电位法的基本特征。在设计有机光电池材料时，最高占据分子轨道(HOMO)和最低空分子轨道(LUMO)之间的能量差(GAP)是一个关键因素。能隙的大小强烈地依赖于Hartree-Fock(HF)交换项与混合密度泛函(DFT)泛函的比率。在普通的混合DFT泛函中，高频交换项比通常是由经验确定的，所有的材料都采用一个常量。相反，依赖于介质的交换电位法对该参数使用依赖于系统的值，该值与介电常数的倒数成正比。本文所研究的有机材料因其材料类型和单位长度的不同而取不同的介电常数值，因此它们的高频交换比也不同。本文讨论了介电相关屏蔽交换势法中能隙、介电常数和HF交换比之间的关系。对于一系列并苯类化合物，研究发现，随着共轭体系的扩展，HOMO-LUMO能隙减小。介电相关的屏蔽交换电位法表明，化合物的介电常数增大，HF交换率降低。对一系列基于噻吩基的给体分子也得到了类似的结果。将计算值与实验测量值进行了比较。我们发现，尽管HOMO-LUMO能隙的理论计算往往高估了实验光学带隙，但如果我们对激子结合能进行修正，则实验值和计算值可以得到更好的符合。
This paper discusses the fundamental features of the dielectric-dependent screened exchange potential approach for organic molecules and photocell materials. The energy difference (gap) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is a key factor when designing organic photocell materials. The magnitude of this energy gap strongly depends on the ratio of the Hartree–Fock (HF) exchange term combined with hybrid density functional theory (DFT) functionals. In ordinary hybrid DFT functionals, the HF exchange term ratio is often determined empirically and a constant value is employed for all materials. Conversely, the dielectric-dependent exchange potential approach employs a system-dependent value for this parameter, which is proportional to the inverse of the dielectric constant. The organic materials examined in this paper take different dielectric constant values according to their material types and unit lengths; therefore, their HF exchange ratios are also different. This paper discusses the relationship between the energy gaps, the dielectric constants, and the HF exchange ratios in the dielectric-dependent screened exchange potential approach. For a series of acene-type compounds, it was found that the HOMO–LUMO gap decreased when their conjugation systems are extended. The dielectric-dependent screened exchange potential approach demonstrated that the values of the dielectric constants of the compounds increased; consequently, the HF exchange ratio decreased. Similar results were obtained for a series of thiophene-based donor molecules. The calculated values were compared with those obtained via experimental measurements. We found that although the theoretical calculations of the HOMO–LUMO gap usually overestimate experimental optical gaps, a better agreement between the experimental and calculated values can be obtained if we correct for the exciton binding energy.