Improved Organic Electrochemical Transistors via Directed Crystallizable Small Molecule Templating

Abstract

Organic electrochemical transistors (OECTs) are of great interest as biosensors and for flexible electronics applications. Historically, processing techniques have been widely used to improve the performance of polymers in organic electronics but have been underutilized in the field of OECTs. Here, we study the effects of a crystallizable small molecule template for improving the performance of poly(3-hexylthiophene-2,5-diyl) (P3HT)-based OECTs. We utilize 1,3,5-trichlorobenzene (TCB) as a crystallizable additive to induce directional crystallization during blade coating. This procedure results in an aligned, highly ordered, and moderately porous layer of the semiconducting polymer. We find that compared to neat P3HT solutions, films cast with TCB additive show a greater than 8× improvement in the steady state figure of merit for OECTs. Additionally, the optimum TCB loading produces anisotropic OECTs where the polymer chain aligned parallel to the current outperforms the perpendicular alignment by more than a factor of 10. We investigated the mechanism of this improvement and found that polymer alignment, polymer ordering, and film porosity all play a role in improving the device performance. Overall, these results demonstrate the importance of processing on the optimization of polymers for OECTs and suggest a route to greatly improve the performance of commercially available hydrophobic polymers.

New Method to Probe the Surface Properties of Polymer Thin Films by Two-Dimensional (2D) Inverse Gas Chromatography (iGC)

“…Conventional column-based iGC has been extensively used for measuring the surface properties of porous media and fibers, and it has been recently used to study the diffusion and permeability of gases through polymer coatings on glass beads . Nevertheless, these methods are limited to powdered samples, while the measurement of 2D materials (i.e., thin films or coatings) is still nascent and being developed. , In this work, we examine the metrology of iGC as applied to the investigation of supported thin films, highlighting a different approach to obtain their thermodynamic properties. Poly­(methyl methacrylate) (PMMA) is used as a model polymer to validate our approach, which encompasses different physical sample forms, ranging from bulk materials to thick films to thin films.…”