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

有机半导体形成光电器件如有机发光二极管、有机太阳能电池和有机场效应晶体管的基础。这些器件非常薄、重量轻且灵活，并且可以在环境条件下通过简单的印刷技术由溶液在大面积上制造。有机电子学中最发达的领域之一是用于移动的电话、平板电脑和电视的基于有机发光二极管（OLED）的显示器;这些对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方法来生产OLED，发射圆偏振光。这个非常简单的方法是将一种传统的发光半导体聚合物与一种螺旋状的分子（螺旋烯）混合。螺旋形分子以某种方式导致意大利面条状聚合物链改变构象，导致聚合物发射圆偏振（CP）光。这种发射CP的OLED在常规OLED显示器、3-D OLED显示器中具有应用，并且作为液晶显示器中的背光。例如，为了提高对比度，大多数显示器包含顶部圆偏振滤光器以去除背反射光。发射CP的OLED将允许所有发射的光通过该滤光片，从而潜在地使显示器的能量效率加倍。这将减少全球能源消耗，延长便携式产品的电池寿命，并延长显示器的寿命。CP发光OLED的其他潜在应用包括生物医学中的蛋白质检测、光学自旋电子学、光学量子计算以及传统和量子光学telecommunication.Despite我们的简单而新颖的方法的成功，我们不明白如何将聚合物与helicene混合导致聚合物结构的变化从而允许其发射CP光的原理。这项资助的目的是真正了解这一过程，确切地了解聚合物结构是如何通过与螺旋烯混合而受到影响的。我们将研究当混合物被加热和冷却时，这种相是如何形成的;这是如何随着聚合物链长和聚合物/螺烯比率而变化的;我们如何通过使用不同溶剂和不同退火处理的溶液加工来产生这种相;是否可以形成螺旋液晶相;以及这些因素如何影响薄膜形态和微观结构。我们还将研究CP光发射过程，研究诸如螺旋烯吸收的CP光是否会导致聚合物的CP发射等因素。特定的半导体聚合物有关（F8 BT）是已知的电子和空穴传输，我们将研究在新的螺旋相的电荷传输。我们将利用所有的工艺知识，创造出一种优化的CP-OLED，具有高CP光输出，亮度和效率。我们还将研究其他类似的半导体聚合物，当与螺旋烯混合时，它们会发射CP光，研究它们的结构，光谱和电子特性。这个项目涉及伦敦帝国理工学院物理和化学系以及谢菲尔德大学材料科学与工程系的团队之间的理想协同作用，前者涵盖光谱，电子和设备测量，后者涵盖结构和形态测量和建模。它还将涉及与剑桥显示技术（英国）的合作伙伴关系，提供高性能聚合物和专业知识，并使技术迅速转移到市场。

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.