Highly Sensitive and Selective Organic Gas Sensors with Surface-Modified Activated Carbon

Organic gas sensors based on conjugated polymers have attracted considerable attention owing to their low operating voltage, mechanical flexibility, and solution processability. However, pristine polymer sensors often suffer from limited gas adsorption sites, insufficient selectivity, and unstable sensing performance under ambient conditions. In this study, surface-modified activated carbon (AC) was incorporated into poly(3-hexylthiophene) (P3HT) to develop highly sensitive and selective organic field-effect transistor-type gas sensors. Activated carbon provides a high-surface-area porous framework, while surface functional groups promote specific interactions with target gas molecules. The surface chemistry of AC was systematically controlled by introducing different functional groups, and the resulting P3HT/AC composite sensors were evaluated toward NO₂, SO₂, and CO₂ gases.

The incorporation of AC significantly improved gas sensing performance compared with pristine P3HT by increasing gas adsorption and enhancing charge modulation in the semiconductor channel. In particular, the N-functionalized AC sensor exhibited the highest NO₂ sensing performance, with a sensitivity of 0.04579 and a low limit of detection of 5.99 × 10⁻⁴ ppm. The S-functionalized AC sensor showed improved SO₂ response, indicating that the surface functionality of AC plays a key role in determining gas selectivity. In addition, the P3HT/AC sensors showed improved ambient and humidity stability compared with pristine P3HT, which is attributed to the preferential adsorption of oxygen and water molecules on the porous AC surface rather than directly on the P3HT channel. These results demonstrate that controlling the surface chemistry of activated carbon is an effective strategy for improving the sensitivity, selectivity, and operational stability of organic gas sensors.