The Effects of Driving Force, Morphology and Anion Separation on Carrier Mobility in Doped Conjugated Polymers

半导体是现代电子产品的基础，例如计算机、平板显示器和移动的电话。大多数半导体都是无机的硬材料，如硅，加工和制造成本很高。该项目探讨了塑料半导体的特性，这些塑料半导体重量轻，灵活，加工成本低。无机半导体的电性能通过掺杂来控制。掺杂是有意将杂质引入半导体中，以改变其电学或光学特性。塑料半导体发展面临的一个关键挑战是它们不像无机半导体那样容易掺杂。该合作项目利用新材料和加工方法可控地掺杂塑料半导体。新材料具有可调特性，这将允许对电导率进行更大程度的控制。新的加工方法允许将掺杂剂分子精确地添加到塑料半导体的所需位置。高质量的掺杂聚合物薄膜将通过一套技术进行研究，以充分了解它们。它们还将被纳入热电设备，将废热转化为电力，这是一种新的可再生能源。本科生和研究生将通过该项目在国家需要的领域接受培训。外联工作将通过示范和实验向洛杉矶地区的高中生介绍可再生能源等相关主题。该项目由材料研究部的电子和光子材料计划和化学部的化学结构、动力学和机制B计划共同资助。共轭聚合物具有许多潜在的用途，因为它们将塑料的机械性能与半导体的电性能联合收割机结合在一起。当通过强氧化剂掺杂时，它们的导电性可以通过数量级来调节，但是与掺杂剂的相互作用以及掺杂剂诱导的形态变化可以限制掺杂的载流子迁移率。该项目利用了顺序处理的优势，其中首先浇铸聚合物膜，并且在第二步骤中从所选择的溶剂中渗透掺杂剂，以适当地溶胀但不溶解下面的聚合物膜。该方法提供了对掺杂聚合物形态的一定程度的控制，使得能够进行大面积应用，例如热电器件。该项目还探索了新型掺杂剂，包括新合成的具有可调氧化还原电位的十二硼烷簇。这些簇具有用于屏蔽聚合物主链上的极化子的抗衡电荷的化学结构，允许控制抗衡离子-极化子相互作用，从而提供改善的载流子迁移率和塞贝克系数。该项目还研究了电荷交换，在反应后，掺杂剂电荷可以通过质量作用取代惰性离子，从而对掺杂共轭聚合物的性质提供另一种程度的控制。在所有情况下，掺杂的聚合物膜的物理结构，如通过掠入射广角X射线散射和中子反射计的组合确定的，与光学和电学性质相关，以理解膜中的电荷的位置如何控制物理性质。最后，该项目使用超快光谱来测量掺杂共轭聚合物薄膜的热导率（通过时域热反射）和电性能（通过泵浦/探测瞬态吸收实验）。该项目的主要目的是确定详细的结构/功能关系，以最大限度地利用掺杂共轭聚合物在热电和其他器件中的应用。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Semiconductors are the basis for modern electronics such as computers, flat screen displays, and mobile phones. Most semiconductors are inorganic, hard materials such as silicon, and are expensive to process and manufacture. This project explores the properties of plastic semiconductors that are lightweight, flexible and potentially inexpensive to process. The electrical properties of inorganic semiconductors are controlled through doping. Doping is the intentional introduction of impurities into a semiconductor for the purpose of changing its electrical or optical properties. A key challenge facing the development of plastic semiconductors is they are not as easy to dope as inorganic semiconductors. This collaborative project takes advantage of new materials and processing methods to controllably dope plastic semiconductors. New materials have tunable properties that will allow for a greater degree of control over electrical conductivity. New processing methods allow dopant molecules to be precisely added to the plastic semiconductors at desired locations. High-quality doped polymer films will be studied by a suite of techniques to fully understand them. They will also be incorporated into thermoelectric devices that convert waste heat into electricity, a new source of renewable energy. Undergraduate and graduate students will be trained in areas of national need through this project. Outreach efforts will introduce high school students in the Los Angeles area to related topics such as renewable energy through demonstrations and experiments. This project is jointly funded by the Electronic and Photonic Materials program of the Division of Materials Research and the Chemical Structure, Dynamics, and Mechanisms B program of the Division of Chemistry. Conjugated polymers have numerous potential uses because they combine the mechanical properties of plastics with the electrical properties of semiconductors. When doped by strong oxidizing agents, their conductivity can be tuned by orders of magnitude, but interactions with the dopant counterion and dopant-induced changes in morphology can limit the doped carrier mobility. This project takes advantage of sequential processing, in which the polymer film is cast first and the dopant is infiltrated in a second step from a solvent chosen to appropriately swell but not dissolve the underlying polymer film. This method provides a degree of control over the doped polymer morphology that enables large-area applications, such as thermoelectric devices. The project also explores novel dopants, including newly-synthesized dodecaborane clusters with tunable redox potentials. These clusters have chemical structures that serve to shield the counterion charge from the polarons on the polymer backbone, allowing for control over the counterion-polaron interaction, and thus providing for improved carrier mobility and Seebeck coefficient. The project also investigates counterion exchange, where after reaction, the dopant counterion can be substituted for an inert ion by mass action, providing yet another degree of control over the properties of doped conjugated polymers. In all cases, the physical structure of the doped polymer film, as determined by a combination of grazing incidence wide angle X-ray scattering and neutron reflectometry, is correlated with the optical and electrical properties to understand how the location of the counterion in the film controls physical properties. Finally, the project uses ultrafast spectroscopy to measure both the thermal conductivity (via time-domain thermal reflectance) and electrical properties (via pump/probe transient absorption experiments) of doped conjugated polymer films. The key aim of the project is to determine detailed structure/function relationships to maximally exploit the use of doped conjugated polymers in thermoelectric and other devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.