Origin of the Strong Induced Chiroptical Effect in Semiconducting Polymer/Helicene Blends

有机半导体构成了有机发光二极管、有机太阳能电池和有机场效应晶体管等光电子器件的基础。这些器件非常薄、轻和灵活，可以在环境条件下通过简单的打印技术从溶液中大面积制造出来。有机电子领域最发达的领域之一是用于手机、平板电脑和电视的基于有机发光二极管(OLED)的显示器；这些领域为价值数十亿美元的全球产业做出了重大贡献。我们最近发现了一种制造OLED的方法，这种OLED发射圆偏振光。这种非常简单的方法包括将一种传统的发光半导体聚合物与一种名为螺烯的螺旋状分子混合。螺旋状的分子以某种方式导致意大利面条状的聚合物链改变构象，导致聚合物发出圆偏振(CP)光。这种CP发射OLED可应用于常规OLED显示器、3D OLED显示器以及作为液晶显示器的背光。例如，为了提高对比度，大多数显示器都包含一个顶部圆偏振滤光片来消除背向反射光。CP发光OLED将允许所有发射的光通过该滤光器，潜在地将显示器的能效提高一倍。这将降低全球能源消耗，延长便携式产品的电池寿命，并延长显示器寿命。CP发光OLED的其他潜在应用包括在生物医学、光学自旋电子学、光学量子计算以及传统和量子光通信中的蛋白质检测。尽管我们简单而新颖的方法取得了成功，但我们并不了解聚合物与螺烯混合如何导致聚合物结构改变，从而使其发射CP光的原理。这项资助的目的是要真正了解这一过程，准确地找出聚合物结构是如何受到与螺烯混合的影响的。我们将研究混合物在加热和冷却时如何形成这种相；它如何随着聚合物链长和聚合物/螺烯比的变化而变化；我们如何通过使用不同的溶剂和不同的退火处理来通过溶液处理来产生这种相；是否可以形成螺旋液晶相；以及这些因素如何影响薄膜的形态和微观结构。我们还将研究CP发光过程，观察诸如被螺烯吸收的CP光是否会导致聚合物的CP发射等因素。这种特殊的半导体聚合物(F8BT)既可以传输电子，也可以传输空穴；我们将研究这种新型螺旋相中的电荷传输。我们将利用所有的工艺知识，创造出优化的CP-OLED，具有高CP光输出、高亮度和高效率。我们还将研究其他类似的半导体聚合物，当它们与螺烯混合时会发出CP光，看看它们的结构、光谱和电子性质。这个项目涉及伦敦帝国理工学院物理和化学系与谢菲尔德大学材料科学与工程系的理想合作，前者涵盖光谱、电子和器件测量，后者涵盖结构和形态测量和建模。它还将与剑桥显示技术公司(英国)建立合作伙伴关系，提供高性能聚合物和专业知识，并使技术能够快速转移到市场。

Organic semiconductors form the basis of optoelectronic devices such as organic light emitting diodes, organic solar cells and organic field-effect transistors. These devices are very thin, lightweight and flexible, and can be fabricated over large areas from solution by simple printing techniques under ambient conditions. One of the most developed areas in organic electronics is that of organic light emitting diode (OLED) based displays for mobile phones, tablets and televisions; these make a major contribution to a multi-billion dollar global industry. We have recently discovered a method to produce an OLED that emits circularly-polarized light. This very simple method involves blending a conventional light emitting semiconducting polymer with a helically shaped molecule known as a helicene. The helically shaped molecule somehow causes the spaghetti-like polymer chains to change conformation, resulting in the polymer emitting circularly-polarized (CP) light. Such a CP emitting OLED has application in conventional OLED displays, 3-D OLED displays, and as backlights in liquid-crystal displays. For example, to improve contrast, most displays contain a top circularly-polarized filter to remove back-reflected light. A CP emitting OLED would allow all the emitted light to pass through this filter, potentially doubling the energy efficiency of the display. This would reduce global energy consumption, increase battery life of portable products, and increase display lifetime. Other potential applications of CP emitting OLEDs include protein detection in biomedicine, optical spintronics, optical quantum computing, and conventional and quantum optical telecommunication.Despite the success of our simple and novel method, we do not understand the principle of how mixing the polymer with the helicene results in a change in the polymers structure allowing it to emit CP light. The purpose of this grant is to actually understand this process, finding out exactly how the polymers structure is affected by blending with the helicene. We will investigate how this phase forms when the mixture is heated and cooled; how this changes with polymer chain length and polymer/helicene ratio; how we can generate this phase by solution processing using different solvents and different annealing treatments; whether a helical liquid crystal phase can form; and how these factors affect thin film morphology and microstructure. We will also investigate the CP light emission process, looking at factors such as whether CP light absorbed by the helicene can result in CP emission from the polymer. The particular semiconducting polymer concerned (F8BT) is known to transport both electrons and holes; we will investigate charge transport in the novel helical phase. We will take all the processing knowledge and create an optimized CP-OLED, with a high CP light output, brightness and efficiency. We will also investigate other similar semiconducting polymers which emit CP light when blended with helicenes, looking at their structural, spectroscopic and electronic properties.This project involves an ideal synergy between teams in the Departments of Physics and Chemistry at Imperial College London and in the Department of Materials Science and Engineering at the University of Sheffield, the former covering spectroscopic, electronic and device measurements and the latter covering structural and morphological measurements and modeling. It will also involve a partnership with Cambridge Display Technology (UK), supplying high performance polymers and expertise, and enabling rapid transfer of the technology towards the marketplace.