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。这些材料的吸引人的特性是，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变得无处不在，高效发光二极管将大幅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，为什么这些应用还没有付诸实践呢？用目前可用的材料制造的设备根本就不够高效。为了理解如何设计出最好的器件材料，我们应该首先了解器件运行的基本电子工艺。其中一个过程是电荷传输：它是所有这些设备运行的核心。我们已经知道了一些关于电荷传输的事情：例如，它是通过分子之间的电荷跳跃进行的，并且它受到无序的严重影响。然而，不幸的是，从分子结构来模拟这种跳跃真的很难。这是因为电荷跳跃受到所有长度尺度上的过程的影响：在分子长度尺度上，它强烈地依赖于相邻分子的取向和位置，而在器件长度尺度上，它依赖于形成良好的传导路径。这意味着，如果我们想定义一个电荷可以跳到上面的分子晶格，我们需要找到一个在原子(0.1-1 nm)和设备(1 Mm)的长度尺度上都准确的晶格表示：这相当于绘制一个高尔夫球场，并准确地确定其中所有草叶的位置和形状！为了克服这些困难，我将使用非常有效的方法来模拟大型分子簇，这要归功于与马克斯·普朗克聚合物研究所的同事们的合作。然后，我将修改模拟电荷传输的方法，以充分利用来自此类形态模型的所有信息，不仅使用分子在这些团簇中的位置和取向，而且还使用这些随时间变化的方式。所有这些方法都将通过在不同材料系统上的声音实验数据进行比较来验证。我将考察三类材料系统，它们都与技术相关：液晶、小分子薄膜，最后是聚合物。本系列文章将让我了解变得越来越复杂的系统。这项研究将使我能够在一个框架内对电荷传输进行建模，在这个框架中，模拟的所有步骤都是合理的，并基于分子计算。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.