聚烷基噻吩纳米线的多晶型结构调控、形成机制及结构-性能关系研究

It is considered that condensed structure control on poly (3-alkylthiophenes) (P3ATs) in nanoscale is essential for the property improvement of the optoelectronic devices. The aggregation of P3ATs in nanoscale generally exhibits the one-dimensional nanowires (NWs) morphology, with the interchain π-π interaction as the main driving force. In recent years, although the high NWs yield and the morphology control can be achieved by several methods, the research on NWs micro-structures which determine the charge transfer efficiency directly receives less attentions. Herein, we propose to control the crystal structures of P3ATs NWs by various methods (including the molecular structure parameters, the crystallization conditions, and the rotation field), and to prepare the NWs films with high crystallinity by vacuum filtration and centrifugation. Structure analysis will be performed further by using complementary synchrotron radiation X-ray diffraction, solid-state NMR and infrared/Raman spectroscopy. The differences of the fine structures for P3ATs NWs obtained through various self-assembly will be revealed. Besides, the control methods for crystal modifications will be constructed. By fabricating the devices for in-situ measurements, we will investigate the formation mechanism of NWs with different condensed structures. Finally, the intrinsic photo conductivities of polymorphic P3ATs NWs will be characterized by terahertz spectroscopy. The structure-property relationship will be constructed. Such studies will be helpful for understanding the crystallization behavior of conductive polymers, providing the theoretical guiance for the structural control of the P3ATs NWs as well as for the optimization of the device properties in the industrial process.

在纳米尺度上调控聚烷基噻吩（P3ATs）的聚集态结构对于提高光电器件性能具有重要意义。以链间π-π作用为主要驱动力，P3ATs在纳米尺度的聚集通常表现为一维纳米线形态。近年来尽管在提高纳米线产率和调控形貌方面取得了进步，但对直接决定电荷传输效率的纳米线微结构研究却没有引起足够重视。本项目拟运用多种手段（分子结构参数、结晶条件、旋转剪切场）调控P3ATs纳米线的晶体结构，并利用真空抽滤、离心方法获得高结晶度纳米线薄膜，在此基础上综合运用同步辐射X-射线衍射、固态核磁、振动光谱等互补的表征技术对样品进行结构解析，研究不同条件下自组装的P3ATs纳米线间精细结构的差异并建立晶型调控方法。同时通过搭建原位测试平台，阐明不同聚集态纳米线的形成机制。最后借助太赫兹光谱技术表征多晶结构纳米线的本征光电导特性，建立结构与性能关系。以上研究将加深我们对梳状高分子结晶行为的理解，并对器件性能优化提供理论指导。

针对聚（3-烷基噻吩）纳米线微结构的调控解析还有待进一步阐明这一现状， 在本基金的资助下，借助固态核磁、X-射线衍射及变温红外光谱技术，在聚烷基噻吩纳米线多晶型结构调控及其形成机制的原位研究方面我们取得了以下6项重要进展: 1）解析了P3BT的多晶型结构，阐明form I与form Iˊ晶型主链存在两种排列，侧链分别为旁式与反式构象，form II晶型主链存在一种排列，侧链同时存在“链间交错”和“非链间交错”；2）考察了侧链长度对四种form I晶型的P3ATs及其共混物（P3AT:PCBM）结构的影响。实验证实更长侧链的P3HT、P3OT和P3DDT form I晶体的晶区只包含packing a，其中P3HT的结晶度最高。与PCBM共混后P3ATs结晶度减少量受侧链长度影响，P3HT下降的最小。此外通过13C-1H 相关谱发现，P3HT:PCBM和P3BT:PCBM存在明显的两相分离结构，而在P3OT:PCBM中两组分达到分子级相容；3）发现了低温溶液老化可制备P3BT form II晶体，该晶体表现为捆束状的纳米晶须形貌，提出了form II向form I的相变机理并非直接的固-固相变，而是需经历无序晶相这一中间过程；4）借助旋转剪切场制备了高产量P3BT form I纳米线，性能测试表明剪切场的施加虽然能够提高纳米线产量，但却降低了纳米线之间的联系，从而对传输性能不利；5）利用低温退火结合自成核方法制备了P3DDT纳米纤维，探究了自成核温度对P3DDT纳米纤维结晶性与晶型的影响。结果表明：P3DDT溶液经过低温退火再室温结晶后可以得到均匀分布的、产率较高的纳米纤维，在此基础上增加自成核步骤能够进一步提高纳米纤维的结晶度。经过低温退火及自成核后制备的样品晶型为form II晶型，而不是通常的form I；6）选用两种溶剂体系制备了P3OT纳米线，实验证实向P3OT/苯甲醚中添加少量氯仿后，得到的纳米线链构象的规整程度更好，π-π相互作用更强，更高的结构规整性导致其热稳定性提高。变温紫外光谱研究证实P3OT在混合溶剂中的结晶行为遵循传统高分子的结晶动力学。以上研究将加深我们对梳状高分子一维结晶行为的理解，并对器件性能优化提供理论指导。