高性能半导体聚合物分子取向和薄膜结构的调控及其电荷输运特性研究

发布时间：2018-05-21 18:54

本文选题：半导体聚合物 + 有机场效应晶体管　；参考：《中国科学技术大学》2017年博士论文

【摘要】：π共轭小分子和聚合物半导体材料已广泛地用于制备有机太阳电池、有机发光二级管(OLED)、有机场效应晶体管(OFET)等器件以及各种类型传感器,在大面积低成本柔性电子学方面展现出巨大的应用潜力。但目前有机半导体材料及其器件还有很多不足之处,例如其载流子迁移率明显仍低于无机半导体材料。这促使人们对涉及其新材料合成、薄膜器件制备以及载流子传输机制等问题做更深入的研究。提高有机电子器件性能的一个关键因素是发展有效的、可规模化的薄膜和器件制备技术,控制有机半导体薄膜微结构特别是分子取向和堆积特性。然而迄今已发展的薄膜结构(特别是宏观取向结构)的调控方法在普适性、规模化和简便性等方面存在许多问题。针对这些问题,在本文的工作中,我们选用P(NDI20D-T2)等几种具有高载流子迁移率的给体-受体(D-A)型共聚物材料作为研究对象,通过发展薄膜制备尤其取向薄膜生长的新方法,调控和优化薄膜的微观结构如分子取向、堆积特性和结晶性等,来提高OFET的器件性能,并探索有机薄膜结构与其电荷输运能力之间的内在关系,取得如下主要研究成果。首先,我们采用强磁场下的溶液涂布方法,实现了对晶态和半晶态聚合物半导体(如D-A型共聚物P(NDI20D-T2)等)薄膜中分子取向和薄膜织构的有效控制,获得大面积高取向的薄膜织构。利用综合性的微结构表征手段,发现取向薄膜内聚合物分子的骨架链是沿着磁场方向择优排列。利用同步辐射掠入射X射线衍射分析从不同的溶剂中磁诱导生长的P(NDI20D-T2)薄膜微结构变化,提出并证实了半导体聚合物薄膜的磁致取向生长的动力学机制,明确了聚合物溶液中的分子聚集态诱发和决定了磁致取向生长的过程。并且通过制备基于强磁场诱导生长的取向薄膜的OTFT器件,发现强磁诱导取向可显著提高聚合物半导体的载流子迁移率(达4倍),实现很高的载流子迁移率各向异性。此外还采用时间调制磁场技术实现了对P (NDI20D-T2)薄膜面外方向分子取向和织构的调控,使分子链间face-on堆积程度显著增强、面外方向结晶性提高,并使面外方向上的电子迁移率提高了近两个量级。同时还深入探究了时间调制磁场调控薄膜结构的过程中,溶液涂布的成膜条件参数(如溶剂、成膜时间等)对分子取向和薄膜织构的影响。上述工作为探索进一步提高高性能D-A共聚物的光电性能提供了新途径,也对深化认识有机材料在强磁诱导下的生长动力学机制和有机薄膜结构与器件性能间的内在关系具有指导性作用。2.为了解决取向薄膜存在的形貌和厚度不均匀性问题,我们首次采用强磁场下的溶剂退火方法,对溶液旋涂沉积的两种D-A型共聚物P(NDI2OD-T2)和DPP2T薄膜进行微结构的调控,实现了大面积高度取向的薄膜织构。通过综合的微结构表征手段,发现采用这一方法制备的聚合物薄膜,不仅形貌和厚度均一性得到改善,并且薄膜中分子取向程度和薄膜结晶性显著地优于磁场下溶液涂布法制备的取向薄膜。同时还研究了磁场下溶剂退火的条件参数对所制备的半导体聚合物薄膜结构和形貌的影响,发现退火时间的延长和高沸点溶剂显著地提高薄膜的分子取向度和结构有序度。基于实验结果,提出了磁诱导的溶剂退火调控聚合物薄膜结构的机理。最后还利用时间调制磁场方法结合溶剂退火调控了 P(NDI2OD-T2)薄膜面外方向的分子取向,提高了薄膜中face-on堆积程度。磁诱导的溶剂退火方法很好地与有机半导体器件制备工艺相兼容,因而将为提高OFET和太阳电池等器件的性能提供了一条很有效的途径。3.采用改进的溶液浸涂法,成功地成长出大面积宏观取向的D-A共聚物P(NDI2OD-T2)和PTHBDTP薄膜。我们利用偏光显微镜、偏振紫外-可见光吸收谱和原子力显微镜等测量技术,发现薄膜中聚合物分子主链骨架沿成膜时液面下移方向择优取向,形成取向的纳米尺度有序晶畴。我们采用固-液界面处的表面张力诱导和溶剂蒸发诱导的分子自组织过程解释了浸涂法生长聚合物取向薄膜的微观机制。使用P(NDI2OD-T2)取向薄膜制备了场效应晶体管,显著地提高了电子迁移率(可达4倍),并实现高达19的载流子各向异性。这可归因于共轭的聚合物主链骨架择优取向引起电荷传导通路的变化。我们提出的简单有效的聚合物成膜方法具有较强的普适性,将在发展低成本、高性能有机电子器件方面具有重要的应用潜力。4.出于降低器件制作成本同时提高器件性能的考虑,我们采用三种D-A共聚物半导体与廉价的聚苯乙烯混合制备半导体/绝缘体共混薄膜,利用共混薄膜制备OFET器件,实现较纯D-A共聚物器件更高的载流子迁移率。然而发现基于不同D-A共聚物制备的共混膜二极管器件,其性能存在巨大的差别。我们采用综合的薄膜结构表征手段研究聚合物共混膜的结构和形貌,发现D-A共聚物自身的分子聚集特性和结晶性对其相应的共混薄膜的微结构具有决定性的影响,进而显著地影响载流子在共混薄膜中不同方向上的传输行为。例如对于结构有序度低的PBDTTT,其PBDTTT/PS薄膜中PBDTTT是均匀分散在整个薄膜中,形成了三维立体的连续的载流子传输通道。而对于结晶有序度高P(NDI2OD-T2)和PDVT,在与PS形成的混合薄膜中,半导体和绝缘体形成明显的分层结构,半导体成分倾向于富集在薄膜表面,这对OFET和二极管这两种不同类型器件的电荷传输产生截然不同的影响。
[Abstract]:Pion conjugated small molecules and polymer semiconductor materials have been widely used in the preparation of organic solar cells, organic light emitting two transistors (OLED), airport effect transistors (OFET) and various types of sensors, which show great potential for application in large area and low cost flexible electronics. However, organic semiconductor materials and their devices are currently used. There are many shortcomings, such as the carrier mobility of the carrier is still lower than the inorganic semiconductor material. This has prompted a more thorough study of the problems involved in the synthesis of new materials, the preparation of thin film devices and the carrier transmission mechanism. And device preparation technology to control the microstructures of organic semiconductor thin films, especially molecular orientation and accumulation characteristics. However, there are many problems in the regulation, scale and simplicity of the developed membrane structures (especially the macro oriented structure). In this paper, we choose P (NDI20D-) T2) several kinds of donor acceptor (D-A) copolymer materials with high carrier mobility are used as the research object. By developing new methods to prepare thin films, the microstructure of the thin films, such as molecular orientation, stacking properties and crystallinity, is regulated and optimized to improve the performance of OFET devices, and to explore the structure and structure of organic films. The intrinsic relationship between the charge transport capacity and the intrinsic relationship of the charge transport capacity is obtained as follows. First, we use the solution coating method under the strong magnetic field to realize the effective control of the molecular orientation and the film texture in the crystalline and semi crystalline polymer semiconductors (such as D-A type copolymer P (NDI20D-T2)), and obtain a large area and high orientation film. By using a comprehensive microstructural characterization method, it is found that the skeleton chain of polymer molecules in the orientation film is optimized along the direction of magnetic field. The microstructural changes of magnetic induced P (NDI20D-T2) films from different solvents are analyzed by synchrotron grazing incidence X ray diffraction, and the magnetization of the semiconductor polymer film is proved and confirmed. The kinetic mechanism of the growth is made clear that the molecular aggregation state in the polymer solution induces and determines the process of magnetic orientation growth. And by preparing the OTFT devices based on the orientation film based on the strong magnetic field, it is found that the strong magnetic induction orientation can significantly increase the carrier mobility of the polymer semiconductor (up to 4 times) and achieve a high load. In addition, the transfer rate of the flow is anisotropic. In addition, the time modulated magnetic field technique is used to control the orientation and texture of the P (NDI20D-T2) thin films. The accumulation of face-on between the molecules is enhanced significantly, the crystallization of the surface is increased, and the electric migration rate in the outside of the plane is increased by nearly two orders of magnitude. In the process of modulating the structure of the thin film by the time modulated magnetic field, the influence of the condition parameters (such as solvent, film forming time) on the molecular orientation and the texture of the film is investigated. The above work provides a new way to further improve the photoelectric properties of high performance D-A copolymers, and also to deepen the understanding of the strong magnetic induction of the organic materials. The intrinsic relationship between the growth kinetics and the structure of the organic film and the performance of the device has a guiding role. In order to solve the problem of the heterogeneity of the morphology and thickness of the orientation films, we used the solvent annealing method under the strong magnetic field for the first time, and the two kinds of D-A type copolymer P (NDI2OD-T2) and DPP2T films deposited by the solution were micro. The large area and highly oriented thin film texture is realized by the structure regulation. By means of comprehensive microstructural characterization, it is found that the polymer films prepared by this method have not only improved the uniformity of the morphology and thickness, but also the degree of molecular orientation and the crystallinity of the film are significantly better than the orientation thinning prepared by the solution coating method under the magnetic field. At the same time, the influence of the condition parameters of solvent annealing on the structure and morphology of the prepared semiconductor polymer film is also studied. It is found that the prolongation of the annealing time and the high boiling point solvent greatly increase the molecular orientation and the structure order of the film. Based on the experimental results, the magnetic induced solvent annealing is proposed to regulate the polymer film. Finally, the molecular orientation of the P (NDI2OD-T2) film is controlled by the time modulated magnetic field method combined with the solvent annealing. The degree of face-on accumulation in the film is improved. The magnetic induced solvent annealing method is well combined with the preparation process of the organic semiconductor device, so it will improve the OFET and solar cells and other devices. The performance of.3. is an effective way to develop a large area macrooriented D-A copolymer P (NDI2OD-T2) and PTHBDTP thin film by improved solution leaching method. We use polarizing microscope, polarization ultraviolet visible absorption spectrum and atomic force microscope to find the backbone of polymer chain in the film. The orientation of nanoscale ordered crystal domains was formed in the direction of the liquid surface movement along the film formation. The micromechanism of the polymer oriented film was explained by the surface tension induction and solvent evaporation induced by the solid liquid interface. The field effect transistors were prepared by using the P (NDI2OD-T2) orientation film. It improves the electron mobility (up to 4 times) and achieves up to 19 of the carrier anisotropy. This is attributable to the change in the charge conduction pathway caused by the preferred orientation of the conjugated polymer backbone. The simple and effective polymer film forming method has a strong universality and will develop low cost and high performance organic electronic devices. In order to reduce the cost of device fabrication and improve the performance of devices, we use three kinds of D-A copolymer semiconductors and cheap polystyrene to prepare semiconductor / insulator blends, and make use of the blend film to prepare OFET devices to realize higher carrier migration than the pure D-A copolymer devices. However, it is found that the properties of the blend membrane diodes based on the different D-A copolymers have great differences. We have studied the structure and morphology of the polymer blends by means of comprehensive thin film characterization, and found that the molecular aggregation and crystallinity of the D-A copolymers have a decisive effect on the microstructure of the corresponding blend films. The qualitative effect has a significant effect on the transport of carriers in different directions in the blend film. For example, for PBDTTT with low structure order, the PBDTTT in the PBDTTT/PS film is uniformly dispersed throughout the film, forming a three-dimensional and continuous carrier transport channel. For crystal order, P (NDI2OD-T2) and PDVT, In the mixed film formed with PS, semiconductors and insulators form a distinct stratified structure, and the semiconductor composition tends to be enriched on the surface of the film, which has a very different effect on the charge transfer of the two different types of devices such as OFET and diode.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O631.1;TB383.2

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