Nelson Jenny, Kwiatkowski Joe J, Kirkpatrick James, Frost Jarvist M
Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, United Kingdom.
Acc Chem Res. 2009 Nov 17;42(11):1768-78. doi: 10.1021/ar900119f.
The performance of an organic photovoltaic cell depends critically on the mobility of charge carriers within the constituent molecular semiconductor materials. However, a complex combination of phenomena that span a range of length and time scales control charge transport in disordered organic semiconductors. As a result, it is difficult to rationalize charge transport properties in terms of material parameters. Until now, efforts to improve charge mobilities in molecular semiconductors have proceeded largely by trial and error rather than through systematic design. However, recent developments have enabled the first predictive simulation studies of charge transport in disordered organic semiconductors. This Account describes a set of computational methods, specifically molecular modeling methods, to simulate molecular packing, quantum chemical calculations of charge transfer rates, and Monte Carlo simulations of charge transport. Using case studies, we show how this combination of methods can reproduce experimental mobilities with few or no fitting parameters. Although currently applied to material systems of high symmetry or well-defined structure, further developments of this approach could address more complex systems such anisotropic or multicomponent solids and conjugated polymers. Even with an approximate treatment of packing disorder, these computational methods simulate experimental mobilities within an order of magnitude at high electric fields. We can both reproduce the relative values of electron and hole mobility in a conjugated small molecule and rationalize those values based on the symmetry of frontier orbitals. Using fully atomistic molecular dynamics simulations of molecular packing, we can quantitatively replicate vertical charge transport along stacks of discotic liquid crystals which vary only in the structure of their side chains. We can reproduce the trends in mobility with molecular weight for self-organizing polymers using a cheap, coarse-grained structural simulation method. Finally, we quantitatively reproduce the field-effect mobility in disordered C60 films. On the basis of these results, we conclude that all of the necessary building blocks are in place for the predictive simulation of charge transport in macromolecular electronic materials and that such methods can be used as a tool toward the future rational design of functional organic electronic materials.
有机光伏电池的性能关键取决于构成分子半导体材料中电荷载流子的迁移率。然而，一系列跨越不同长度和时间尺度的复杂现象组合控制着无序有机半导体中的电荷传输。因此，很难根据材料参数来合理地解释电荷传输特性。到目前为止，提高分子半导体中电荷迁移率的努力主要是通过反复试验，而不是通过系统设计。不过，最近的进展使得对无序有机半导体中电荷传输进行首次预测性模拟研究成为可能。本综述介绍了一组计算方法，特别是分子建模方法，用于模拟分子堆积、电荷转移速率的量子化学计算以及电荷传输的蒙特卡罗模拟。通过案例研究，我们展示了这种方法组合如何能够在很少或没有拟合参数的情况下重现实验迁移率。尽管目前该方法应用于高对称性或结构明确的材料体系，但这种方法的进一步发展可以解决更复杂的体系，如各向异性或多组分固体以及共轭聚合物。即使对堆积无序进行近似处理，这些计算方法在高电场下也能将实验迁移率模拟在一个数量级范围内。我们既能重现共轭小分子中电子和空穴迁移率的相对值，又能根据前沿轨道的对称性对这些值做出合理的解释。通过对分子堆积进行全原子分子动力学模拟，我们可以定量地复制沿盘状液晶堆叠的垂直电荷传输，这些盘状液晶仅在侧链结构上有所不同。我们可以使用一种廉价的、粗粒度的结构模拟方法重现自组装聚合物迁移率随分子量的变化趋势。最后，我们定量地重现了无序C60薄膜中的场效应迁移率。基于这些结果，我们得出结论，对于高分子电子材料中电荷传输的预测性模拟，所有必要的组成部分都已具备，并且这些方法可以用作未来功能性有机电子材料合理设计的工具。
