Speaker
Description
Not only are thin films of organic semiconducting polymers on flexible plastic substrates (such as polyethylene terephthalate, PET) suitable to several applications in organic electronics, but they also present intriguing mechanical properties due to their variable degree of crystallinity, thickness, and stacking of polymer chains. These properties are controlled by the degree of tacticity of the polymer, preferential alignment of the polymer by the substrate surface, and -electron related van der Waals interactions between polymer repeating units belonging to different polymer filaments. Nonetheless, the effect of substrate folding on the mechanical properties of organic semiconducting polymer thin films are poorly understood because of the lack of detailed structure-function relationship studies. In this study, we will use a multi-technique approach based on atomic force microscopy, Raman spectroscopy and X-ray diffraction to investigate the role of substrate folding in the formation of ridges on organic thin films of poly(3-hexylthiophene) (P3HT) at different thickness, concentration of crystallization additives (including 1-dodecanethiol), and annealing temperature. Through Raman spectroscopy, we find that ridges formed upon bending may be either more crystalline or more disordered than the surrounding layer depending on the additive concentration. It is also found that taller and more prominent ridges are formed at increasing concentrations (up to 10% vol) of crystallization additive upon first-time folding of the polymeric thin film, while second-time bending in the orthogonal direction leads to shorter and less prominent ridges. This phenomenology may be the result of the interplay of shear-induced amorphization and additional crystallization due to 1-dodecanethiol diffusion in P3HT upon bending. Possible models towards the understanding of these phenomena will be discussed. Collectively, our work elucidates the critical role of mechanical properties of organic polymer thin films for their applications in flexible electronics devices, such as organic photovoltaics, light emitting diodes and thermoelectric generators.
| Keyword-1 | Organic semiconducting polymer |
|---|---|
| Keyword-2 | Mechanical deformation |
| Keyword-3 | Thin-film mechanics |