（缺电子杂环-噻吩）共聚的p-型高分子/n-型小分子双组分体系的表面自组装研究:结构调控及p-n分子堆积方式与轨道能级匹配对其界面电学性质的影响

Tuning the surface assemblies of p-type/n-type bicomponent systems and exploring the electronic properties at p-n molecular interfaces play significant roles in varied fundamental researches of surface assembly such as understanding the nature of assorted noncovalent interactions and their fine balances, disclosing the assembling behaviors and principles in complex and life environments, as well as sorts of applications including assembly functionalization, molecular and organic electronics development. Currently most of researches were carried out in high vacuum, therefore both p-type and n-type compounds are limited to small molecules. Semiconductor polymers are very few involved in these studies although they are as important as small molecules to the development of molecular and organic electronics. In this project, surface assemblies of p-type poly(electron-deficient heterocyclic unit-thiophene) compounds/n-type small molecules will be investigated in detail. The p-type polymers and n-type small molecules in this project are designed with great care. Different electron-deficient units are used to tune the orbital positions of p-type polymers gradually. We choose two kinds of n-type small molecules whose highest occupied molecular orbital (HOMO) positions are close to each other but their lowest unoccupied molecular orbital (LUMO) positions are different. Thus, in our systems, the matching of orbital levels between p-type and n-type component will be adjusted systematically. Furthermore, only one kind of n-type molecule can possibly forms hydrogen bond with p-type polymers, indicating that the interactions of p-type polymers with two kinds of n-type compounds differ very much. Thus, in this project, we will 1) systematically tune the assembling structures of p-type polymer/n-type small molecule bicomponent systems through adjusting the properties of solvents and annealing parameters; 2) reveal the assembling structures and stacking fashions of p-n molecules with scanning tunneling microscopy, theoretical calculation and simulations; understand the effect of the noncovalent interactions between p-type and n-type molecules on the formation and transformation of surface assemblies and the features of thermodynamic favorable structures; 3) characterize the electronic properties at p-n molecular interfaces including energy level alignment, tunneling process etc. through X-ray/ultraviolet photoelectron spectroscopy, scanning tunneling spectroscopy and theoretical calculations etc.; and analyze the influence of orbital matching and stacking styles of p-n molecules on its interface electronic properties. The results will provide fundamental supports for rational tuning and fabrication of bicomponent surface assemblies, and for developing molecular/organic electronics in a fast yet low cost solution method in future.

p-型/n-型双组分表面自组装层的结构调控及其界面电学性质研究,对理解自组装领域中的基本科学问题有重要意义，也与分子及有机电子学的发展密切相关。目前，对小分子体系的研究取得了丰富的结果，但对聚合物体系研究较少。我们选择了（缺电子杂环-噻吩）共聚的p-型高分子，利用缺电子杂环有序地调节聚合物的能级位置；选择HOMO接近、LUMO位置不同的两类n-型小分子，但只有一类n-型小分子可以形成氢键。据此，有规律地调节p-n分子间的能级匹配与作用力。我们将：1）利用溶剂性质、高温退火等调控组装结构；2）通过扫描隧道显微镜、理论计算与模拟等表征组装结构，揭示p-n分子间的堆积方式；理解分子间作用力对组装结构的形成、演化及最终热力学稳定组装结构的影响；3）利用光电子能谱、扫描隧道谱、理论计算等考察p-n分子界面上的能级排布、电子隧穿等电学性质，并分析界面电学性质与p-n分子间堆积方式、能级匹配的关系。

在项目中，我们从只有聚合物的单组分体系入手，逐步扩展到了复杂的小分子/聚合物双组份体系，并将研究提升到了器件层面。在第一部分研究中，首先考察了溶剂性质对聚合物表面吸附结构结晶性的影响，发现高沸点溶剂有利于形成高结晶性的组装结构；在溶剂沸点相差不大时，溶剂与聚合物的相溶性不同，聚合物在溶液中的构象也有所区别，导致了存在两种竞争成膜机制：溶液中的无序聚集体直接吸附和表面自组装成膜，而后者更有利于结晶畴区的形成。除了溶剂，热退火也是调控聚合物薄膜及器件结构与性能的常用手段。在热退火过程中，聚合物表面吸附层的结构演化与薄膜中远离基底的本体层部分有明显的区别，基底对聚合物结晶过程有促进作用。通过实时跟踪发现了柔性聚合物畴区在表面运动的各项异性特征、较长时间的类弹性运动机制、新颖的变形虫式、蠕虫式及分子桥介导的运动模式，这些都与刚性球形颗粒在三维液体中的经典布朗运动有显著地区别。在第一部分研究工作的基础上，开展了对小分子/聚合物双组份体系的研究。发现能量最低是理解或预测热处理所形成的稳定结构的重要依据；并表明小分子在聚合物烷基链与基底间的插入对聚合物表面吸附构象由反式到顺式的翻转具有显著地催化作用。催化机制在于小分子的插入大大减弱了烷基链与基底间的相互作用。界面性质研究表明当小分子与聚合物形成平面型堆积时它们之间没有明显的电学性质耦合。进而，我们将研究内容提升到了器件层面。通过不同方式构筑了多种聚合物（小分子）/石墨烯复合薄膜，并详细地考察了热退火对其结构与光电探测性能的调控作用。发展了具有高效、宽频或波长敏感性、快速开关能力的光电探测器，并分析了有机-石墨烯界面层结构与性能对器件光电探测性能的影响。项目中的研究工作为精确地理解聚合物薄膜的结构演化趋势、高效调控聚合物光电器件的性能等有重要的参考价值。