It has been a long-term goal to understand the molecular orientation in films of conjugated polymers, which is crucial to their efficient exploitation. Here, we show that the surface energies determine the crystal orientation in films of model conjugated polymers, substituted polythiophenes crystallized on substrates. We systematically increase the surface energy of edge-on crystals formed at the vacuum interface by attaching polar groups to the ends of the polymer side chains. This suppresses crystallization at the vacuum interface, resulting in a uniform face-on crystal orientation induced by the graphene substrate in polythiophene films as thick as 200 nm, which is relevant for devices. Surprisingly, face-on crystal orientation is attained in the modified polythiophenes crystallized even on amorphous surfaces. Furthermore, for the samples with still competing interfacial interactions, the crystal orientation can be switched in the same sample, depending on the crystallization conditions. Thus, we report a fundamental understanding and control of the equilibrium crystal orientation in films of conjugated polymers.

中文翻译：

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通过调节表面能来控制共轭聚合物薄膜中的晶体取向


了解共轭聚合物薄膜中的分子取向一直是一个长期目标，这对于其有效利用至关重要。在这里，我们表明表面能决定了模型共轭聚合物（在衬底上结晶的取代聚噻吩）薄膜中的晶体取向。我们通过将极性基团连接到聚合物侧链的末端，系统地增加了在真空界面处形成的边缘晶体的表面能。这抑制了真空界面处的结晶，从而在厚达 200 nm 的聚噻吩薄膜中由石墨烯衬底诱导出均匀的正面晶体取向，这与器件相关。令人惊讶的是，即使在无定形表面上结晶的改性聚噻吩中也能实现正面晶体取向。此外，对于仍然存在竞争界面相互作用的样品，可以根据结晶条件在同一样品中切换晶体取向。因此，我们报告了对共轭聚合物薄膜中平衡晶体取向的基本理解和控制。