Molecular Modelling of Charge Transport in Conjugated Materials.

近年来，有机材料在电子领域的应用已成为一个非常有前途的技术领域。这些材料的诱人之处在于，它们可以让我们使用非常廉价的制造技术来生产电子设备。这将为具有革命性潜力的应用开辟道路：廉价的太阳能电池将无处不在，高效率的发光二极管将大大降低我们的能源账单，廉价的晶体管将使智能电子产品集成到我们的生活环境中。那么，为什么这些应用没有付诸实践呢？用目前可用的材料制造的设备根本不够高效。为了了解如何为设备设计最好的材料，我们应该首先了解设备操作的基本电子过程。其中一个过程是电荷传输：它是所有这些设备运行的核心。我们已经知道一些关于电荷传输的事情：例如，它是通过分子间的电荷跳跃来进行的，并且它受到无序性的严重影响。然而，不幸的是，从分子的结构来模拟这种跳跃是非常棘手的。这是因为电荷跳跃在所有长度尺度上都受到过程的影响：在分子长度尺度上，它强烈依赖于邻近分子的方向和位置，而在器件长度尺度上，它依赖于良好传导途径的形成。这意味着，如果我们想要定义一个电荷可以跳跃的分子晶格，我们需要找到一个在原子长度尺度（0.1 - 1nm）和设备长度尺度（1mm）上都精确的晶格表示：这相当于画一个高尔夫球场，并得到其中所有草叶的位置和形状完全正确！为了克服这些困难，我将使用非常有效的方法来模拟大分子簇，这要感谢马克斯普朗克聚合物研究所的同事们的合作。然后，我将修改模拟电荷输运的方法，以充分利用来自这些形态学模型的所有信息，不仅使用这些簇中分子的位置和方向，而且还使用它们随时间变化的方式。所有这些方法都将通过与不同材料体系的可靠实验数据的比较来验证。我将看三种材料系统，它们都与技术相关：液晶，小分子薄膜，最后是聚合物。这个系列将让我看到越来越复杂的系统。这项研究将允许我在一个框架中模拟电荷传输，在这个框架中，模拟的所有步骤都是合理的，并且基于分子计算。这将使我更好地理解材料的化学和物理性质对电荷迁移率的作用。

In recent years, the use of organic materials in electronics has become a very promising technological area. The attractive property of these materials is that they could allow us to use very cheap manufacturing techniques to produce electronic devices. This would open the way to applications with revolutionary potential: cheap solar cells would become ubiquitous, high efficiency light emitting diodes would drastically lower our energy bills, cheap transistors would allow integration of smart electronics in our living environments.So why have these applications not been put into practice? Devices manufactured from currently available materials are simply not efficient enough. In order to understand how to design the best possible materials for devices, we ought to first understand the fundamental electronic processes underlying the operation of a device. One of such processes is charge transport: it is at the heart of the operation of all these devices. We already know some things about charge transport: that it proceeds by charges hopping between molecules and that it is heavily affected by disorder, for example. Unfortunately, however, it is really tricky to model this hopping from the structure of the molecules. This is because charge hopping is affected by processes at all length scales: at the molecular length scale it is strongly dependent on the orientation and position of neighbouring molecules, and on the device length scale it is dependent on the formation of good pathways for conduction. This means that if we want to define a lattice of molecules that charges can hop on, we need to find a representation of the lattice that is accurate both on the length scale of an atom (0.1 - 1 nm) and on the length scale of a device (1mm): this is equivalent to drawing a golf course and getting the position and shape of all the blades of grass in it exactly right!To overcome these difficulties, I am going to use very efficient methods to simulate large clusters of molecules, thanks to a collaboration with colleagues at the Max Planck Institute for Polymer Research. I am then going to modify the methods to simulate charge transport to take full advantage of all the information from such morphology models, using not only the positions and orientations of molecules in these clusters, but also the way these vary in time. All these methods are going to be validated by comparison with sound experimental data on different material systems. I will look at three classes of material systems, all of which have technological relevance: liquid crystals, films of small molecules and finally polymers. This series will allow me to look at systems which are becoming increasingly complex. This research will allow me to model charge transport in a framework where all the steps of the simulation are soundly justified and based on molecular calculations. This will allow me to better understand the role that the chemical and physical properties of a materials have on charge mobility.