Elucidating the Effect of Interfacial Interactions on Crystal Orientations in Thin Films of Polythiophenes

Abstract

Molecular orientation is crucial for improving the efficiency of organic electronic devices. In many ordered materials, orientation is achieved by directional crystallization on a substrate but usually not in semicrystalline conjugated polymers. Specifically, a full face-on molecular alignment of poly(3-hexylthiophene) (P3HT) on a substrate has not been realized so far. Here, it is found that P3HT crystallized on graphene exhibits a double-layered edge-on and face-on crystal orientation with edge-on crystals formed on the top surface. This finding is interpreted as a result of two competing interfacial interactions of P3HT chains with graphene and vacuum. By modifying the side-chain chemical composition in poly [3-(6-bromohexyl)]thiophene, the influence of the interface to vacuum can be reduced, resulting in full face-on orientation in films with a thickness of up to 26 nm. These results demonstrate that directed crystallization can be used to control the orientation of semicrystalline functional polymers in thin films given that the interaction with both interfaces is taken into account.

Influence of Tacticity on the Structure Formation of Poly(methacrylic acid) in Langmuir/Langmuir–Blodgett and Thin Films

“…The obtained detector image was converted to the reciprocal coordinates according to the literature. [56,57]…”

Direct Observation of Two-Step, Stratified Crystallization and Morphology in Conjugated Polymer Thin Films

“…45 Surface freezing has been proposed to explain ex situ preferential orientation near the surface of P3HT films, but has not been directly observed in situ. 43,44 Overall, the role of the air−polymer interface on the melt-crystallization process at various film depths remains elusive.…”

Highly Efficient Supramolecular Nucleating Agents for Poly(3-hexylthiophene)

“…Semiconducting semi-crystalline polymers are an established class of materials combining polymer science and technology with optoelectronics and photophysics. , These materials are of particular interest in thin-film architectures processed from solution. , Controlling the morphology, i.e., the relationship between the highly ordered crystalline domains and the entangled disordered amorphous phase, plays a decisive role in the optical and electronic characteristics and, ultimately, the device performance. ,− In general, the solid-state morphology can be controlled mainly by changes to the nucleation and crystal growth process. A multitude of approaches have evolved in this context, including thermal and solvent vapor annealing, solvent evaporation control and antisolvent usage, as well as processing additives , and nucleating agents …”