【作者】 田雪雁；

【导师】 徐征；

【作者基本信息】 北京交通大学 ， 光学工程， 2010， 博士

【摘要】 共轭高分子具有机械性能好,热稳定性高,可溶性好,液相成膜简单,制备成本低,适合于制备大面积柔性器件等优点,高分子有机场效应晶体管(OFET)及其应用被认为是未来有机微电子学的发展方向及有机电子商业研究的热点。为了突破高分子OFET场效应迁移率低及载流子传输机制匮乏两个重大难题,本论文深入研究了以高度区域规则的聚(3-己基噻吩)(RR-P3HT)为代表的有机高分子半导体层本身微观自组织理论和机理这一前沿课题,从根本上发掘有机高分子半导体载流子传输机制及利用其来指导高性能高分子OFET的设计及制备。本论文具体研究工作及成果如下：首先,工作中采用同步辐射掠入射X射线衍射技术,研究了高分子OFET中以RR-P3HT为半导体层的结晶行为及微观结构组织变化,及其引起的高分子半导体电荷传输机制,并且由此推导高分子自组织机制与迁移率的关联性。研究发现,采用自组装单分子层(SAMs)技术进行界面修饰,可以完善绝缘层与RR-P3HT半导体层之间的界面效果。SAMs的形成改善了界面,可以有效地控制上层RR-P3HT半导体层的结晶性及微观结构,使较多的噻吩环面垂直于衬底、得到π-π堆积方向平行于衬底的二维微晶粒薄片结构,这种微观结构有效地形成了二维共轭电荷传输通道,完善了在RR-P3HT工作层生长过程中的自组织机制；热退火改善了RR-P3HT薄膜生长过程中的自组织过程；并且对于RR-P3HT半导体工作层来说,慢速生长过程比快速生长过程更有利于有效的二维共轭微晶粒薄片生长,更能完善RR-P3HT工作层生长过程中的自组织机制。其次,利用有效的物理及化学手段进一步调控了RR-P3HT自组织机制,用来提高以RR-P3HT为半导体层的高分子OFET的器件性能,尤其是场效应迁移率。(一)利用界面修饰效应完善自组织机制,来提高高分子OFET器件性能的研究。采用六甲基二硅胺烷HMDS修饰了高分子OFET绝缘层与半导体层之间的界面,提高了高分子OFET的器件性能,并对其性能改善机制进行了深入地研究。由于SAMs修饰的化学过程及其引起的表面物理性能的有效变化,促进了RR-P3HT自组织过程中理想微晶粒薄片的形成及较佳分子的取向排列,最终有利于RR-P3HT OFET器件性能的提升。另外,对修饰作用下的高分子OFET中RR-P3HT的薄膜形态与电荷传输性能关系进行了细致地研究。从薄膜表面形貌变化及结晶两个方面充分地证实了不同液相制膜方法及滴膜法制备非均匀性的高分子OFET的电荷传输性能。工作中对快慢速生长的RR-P3HT薄膜的不同形貌及结晶情况进行了比较,验证了慢速生长的滴膜法制备的RR-P3HT薄膜中“纤维状”薄膜形貌较快速生长的旋涂法制备的“蠕虫状”形貌更有利于载流子的传输。(二)进行了利用热退火效应与静置作用完善自组织机制,来提高高分子OFET器件性能的研究。研究发现,真空静置及热退火后处理对高分子RR-P3HT工作层的微晶粒结构与分子排列取向,表面形貌及电荷载流子迁移率的影响很大。快慢速生长液相制膜方式得到的实验结果比较一致。研究认为合适的退火处理(150℃热退火)及长时间的真空静置,将有利于高分子自组织过程中理想微晶粒结构的形成,高分子分子的连接及取向,结果导致器件迁移率的提升。(三)利用改善低温溶液处理完善自组织机制,来提高高分子OFET器件性能的研究。在低温下完善溶液性质,利用优化浓度与非溶剂掺杂完善自组织机制,来得到质量良好的高分子RR-P3HT半导体薄膜,从而改善高分子OFET器件性能。研究发现,随着RR-P3HT在氯仿溶剂中重量百分比的增加,形成了更多理想结构的微晶粒薄片及更大的纳米岛状物,其高分子RR-P3HT OFET的性能得到了较大地提升。基于表面形貌及电学性能的测试结果,我们认为载流子迁移率与有机工作层的表面形貌及薄膜厚度有着密切的关联性。并且发现一定范围内,高分子(RR-P3HT)与小分子(并五苯)DFET中表面形貌及载流子迁移率的厚度依赖性存在明显区别。另外,用乙醇及乙腈非溶剂进行适量的掺杂,将完善高分子自组织机制,导致高分子OFET电学性能的提升。更多还原

【Abstract】 Polymer organic field-effect transistors (OFET) are regarded as the most promising technology of microelectronics and organic electronics due toπ-conjugated polymer possessing excellent mechanical property, reasonable thermal stability, easy solution-processability, large coverage area, flexibility of device, and potential cost advantage. However, at present, the low mobility and deficient conduction of polymer OFET limit their applications. In order to improve their properties, the mechanism of microstructure self-organization of organic semiconductor that is regioregular poly(3-hexylthiophene) (RR-P3HT) of polymer OFET is investigated in this thesis. The conduction mechanisms of polymer are revealed, which provides a theoretical guidance to design and prepare polymer OFET with high performance in the future. Detail researches and results are as follows:Firstly, the crystallization action, the microstructure change of self-organization and the resulted conduction mechanisms of polymer semiconductor active thin layer in polymer OFET are investigated by synchrotron radiation grazing incident X-ray diffraction (GIXRD) for understanding the relationships between polymer self-organization and charge carrier mobility.The results indicate that self-assembled monolayers (SAMs) as the modified layer significantly improve the interface quality between the insulator layer and the organic semiconductor layer that is RR-P3HT. The change of the crystalline microstructure of RR-P3HT clarifies the effect of SAMs for improving the interface between the insulator layer and the organic semiconductor layer. The self-organiztion of RR-P3HT modified by SAMs improves the crystalliztion to pack form the thiophene rings along the perpendicular direction of substrate and results that theπ-πinterchains are stacked to parallel the substrate. The two-dimensional charge transport is improved. In addition, annealing under a suitable temperature can facilitate the process of self-organization of polymer thin film. Furthermore, we find that two-dimensional, conjugated, and self-organized crystalline lamellae are easier gained with slow grown film than with fast grown film.Secondly, the self-organization process is controlled by effective physical and chemical means to improve the performance of RR-P3HT OFET, especially the field-effect mobility. (1) Self-organization is improved by interface modification to enhance the performance of RR-P3HT OFET and the mechanism is investigated. Hexamethyldisilizane is used as the modification solution. The effective change of chemical processes and surface physical properties by SAMs modification, which favor for self-organized crystalline lamellae and molecule orientation, results in the enhancement of the performance of RR-P3HT OFET. In addition, the relationship between the morphology and charge transport properties of RR-P3HT is investigated in details. Charge transport properties of RR-P3HT deposited by different methods and the homogenization of drop-cast film are proved by measurements of surface morphology and crystallization. It is concluded that well-defined fibrillar morphology of drop-cast slow grown film is favored to charge transport, comparing worm morphology of spin-coat fast grown film.(2) Self-organization is improved by thermal annealing to enhance the performance of RR-P3HT OFET. We find that the crystal structure, the molecules interconnection, the surface morphology, and the charge carrier mobility of polymer films are affected by vacuum relaxation and annealing at suitable temperature (150℃) which facilitate the structure of RR-P3HT and result in the enhancement of field-effect mobility.(3) Self-organization is improved by low temperature solution-process to enhance the performance of RR-P3HT OFET. At low temperature, RR-P3HT solution properties are improved by optimizing concentration and non-solvent addition, and the quality of polymer film and the performance RR-P3HT OFET are improved. The results indicate that the performance of RR-P3HT OFET is improved drastically with the increase of RR-P3HT weight percentages in chloroform solution due to the formation of more microcrystalline lamellae and bigger nanoscale islands. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility depends on the morphology and thickness of organic active layer. Furthermore, we demonstrate that the thickness dependence of surface morphology and charge carrier mobility in polymer (RR-P3HT) OFET and small molecule (pentacene) OFET are different. In addition, an appropriate non-solvent addition (acetonitrile and ethanol) can improve the self-organization of polymer semiconductor layer, resulting in performance enhancement of polymer OFET.更多还原