Porous Semiconducting Polymeric Films for High Performance Organic Electrochemical Transistors (OECTs)

Organic electrochemical transistors (OECTs) have attracted attention due to their low-cost fabrication, biocompatibility, high transconductance, low operational voltages, and mixed ionic-electronic conduction. These features make them ideal for bioelectronic applications. However, OECTs face limitations in kinetic performance, which hampers their ability to detect fast biological events. This thesis focuses on improving OECT doping kinetics by introducing porosity into the polymer channel. The material studied is poly(3-hexylthiophene) (P3HT). The hypothesis is that porous P3HT channels, with their increased surface area, enhance ionic mobility, thus improving the device kinetic response. The breath figure method was explored and found to be the only effective and reproducible approach to achieve porosity, particularly when optimizing solvent type, relative humidity, spin coating, and polymer solution concentration. The doping kinetics of the porous films were analyzed using time-resolved Vis-NIR absorbance spectroelectrochemistry. Unexpectedly, the porous films exhibited slower doping kinetics compared to dense, non-porous films. This can be explained by the lower thickness and increased crystallinity in dense films, which enhances electron mobility, offsetting the advantages of higher ionic mobility provided by the porosity. Additionally, pore arrangement and coverage were found to influence performance. Films with a linear pore structure displayed faster doping kinetics than those with a honeycomb-like porous structure, suggesting that specific pore geometries facilitate more efficient electron transport. Despite the slower doping kinetics observed in porous P3HT films, this study successfully identified a reproducible method for fabricating porous films. This research serves as a foundation for future work aimed at optimizing the morphology of semiconducting polymer films to enhance OECT performance, with potential applications in biosensing and bioelectronics.