Polymer Semiconductor Crystallization: The Oligomer "Bottom-Up" Approach

技术综述烷基取代的聚噻吩类聚合物半导体因其可溶液处理的性质以及在晶体管和太阳能电池等器件中的应用而成为人们感兴趣的焦点。然而，它们的载流子迁移率明显低于五苯并五烯和Rubrene等小分子半导体。较低的迁移率可归因于与缠绕的高分子链相关的结构无序，这些结构无序导致较小且排列较少的晶体在薄膜中形成晶界。为了让聚合物半导体的性能超过小分子半导体，并使其应用于现实世界，必须首先开发一种制造高结晶薄膜的协议。这项研究的目的是通过使用低分子聚合物或低聚物来开发一种结晶协议。我们的目的是从这些材料中发展出结构-性质关系，并确定这类低聚物的电子和分子性质。该项目的方法是从基准构造物十二烷基季戊四烯合成一系列低聚物，然后利用偶合化学合成共轭长度可控、多分散性窄的低分子量低聚物。PI还将利用低聚物单晶膜作为测试结构，用于测量场效应晶体管中的本征载流子迁移率。该计划的科学成果将是对低分子量聚合物中链堆积的基本了解。这些知识将帮助人们理解并最终控制高分子量聚合物的结晶。这项工作还将影响人们如何设计具有可控分子量和窄多分散性的聚合物，以生长高度结晶的薄膜。非技术概述分子如何在聚合物半导体晶体中排列的基础知识对于理解聚合物薄膜和器件中的电输运将是至关重要的。该项目描述的方法结合了通过化学方法创造新材料、晶体生长、器件制造方面的专业知识以及解决问题的跨学科方法，旨在了解和优化聚合物/有机电子设备的运行方式。这项研究计划的成功将对我们在纳米尺度和本体长度尺度上对聚合物结晶的基本理解具有重要意义。拟议的研究将提供机会，在合成、聚合物科学和器件制造方面培训博士后、研究生和本科生。首席调查员(PI)布里塞诺还将参与对社会、科学界和全国贫困学生产生更广泛影响的专业活动。

TECHNICAL SUMMARYPolymer semiconductors such as the alkyl-substituted polythiophenes have been the focus of interest because of their solution-processable nature and application in devices such as transistors and solar cells. Their carrier mobilities, however, are significantly lower than small-molecule semiconductors such as pentacene and rubrene. The lower mobility is attributed to the structural disorder associated with entangled polymer chains which result in smaller and less-aligned crystals that form grain boundaries in thin films. In order for polymer semiconductors to outperform small-molecule semiconductors and make their way to real world applications, a protocol for fabricating highly crystalline films must first be developed. The objective of this study is to develop a crystallization protocol by employing low molecular weight polymers, or oligomers. Our intent is to develop a structure-property relationship from these materials and determine the electronic and molecular properties of this class of oligomers. The approach to this project is to synthesize a series of oligomers from the benchmark building block, didodecylquaterthiophene, and then employ coupling chemistry to produce low molecular weight oligomers with well-controlled conjugation lengths and narrow polydispersities. The PI will also utilize oligomer single-crystalline films as test structures for measuring intrinsic carrier mobilities in field-effect transistors. The scientific outcome of the program will be a fundamental understanding of chain packing in low molecular weight polymers. This knowledge will help one to understand and ultimately control crystallization in higher molecular weight polymers. This work will also impact on how one can design polymers with controlled molecular weights and narrow polydispersities for growing highly crystalline films. NON-TECHNICAL SUMMARYFundamental knowledge of how molecules are arranged in polymer semiconductor crystals will be critical for the understanding of electrical transport in polymer thin films and devices. The approaches described in this project combine creation of new materials by chemical means, expertise in crystal growth, device fabrication, and an interdisciplinary way of solving problems, and are aimed toward understanding and optimization of how polymeric/organic electronic devices operate. The success of the proposed research program would be of importance toward our fundamental understanding of polymer crystallization on both the nano- and bulk length scales. The proposed studies will offer opportunities to train postdoctoral, graduate, and undergraduate students in synthesis, polymer science, and device fabrication. Principal Investigator (PI) Briseno will also be engaged in professional activities that have broader impact on society, the scientific community, and underprivileged students across the nation.