Low-Regioregularity Polythiophene for a Highly Sensitive and Stretchable Gas Sensor

Abstract

In this study, we examined how the regioregularity ofpoly(3-hexylthiophene)(P3HT) affects molecular packing, free volume, charge transport, andgas sensing properties. Our results showed that the presence of regularalkyl side chains on the polymer backbone promoted a high degree ofstructural order in regioregular P3HT molecules, leading to a compactpacking density and reduced free volume. Consequently, it was morechallenging for NO2 molecules to interact with the holecharge carriers in the conductive channel. On the other hand, theregiorandom P3HT films displayed a larger free volume, attributedto the irregular side chains, which facilitated the gas-analyteinteraction while impeding efficient charge transport. Thus, thesefilms exhibited greater sensitivity to analyte gas molecules. Themolecular order, packing density, and hardness of P3HT films wereconfirmed through the use of multiple techniques, including UV-visspectroscopy, atomic force microscopy, and grazing-incidence X-raydiffraction. Additionally, the regiorandom P3HT films showed enhancedmechanical flexibility compared to the regioregular films. In conclusion,our findings emphasize that the regularity of polymer molecules playsa significant role in determining the charge carrier transport andgas adsorption characteristics.