Addition of en-APTAS to a Polythiophene Film for Enhanced NO₂ Gas Sensing

With the aim of enhancing gas-sensor performance, we introduced N-[3-(trimethoxysilyl)propyl]ethylenediamine (en-APTAS) into poly(3-hexylthiophene) (P3HT) thin films. The P3HT films with en-APTAS as an additive showed superior gas-sensing performance compared with pristine P3HT films. The sensitivity of the gas sensor with en-APTAS was especially enhanced for NO2 gas because the en-APTAS has two amine groups that act as adsorption sites for NO2 gas molecules as a consequence of their strong binding energy. The P3HT film with 0.5 vol % en-APTAS fabricated on a OH-functionalized substrate exhibited the greatest responsivity (ΔID/I0 = 0.83) and highest response, recovery rates (ΔR/Δt = 0.26 and 0.004, respectively), and sensitivity (2.9%/ppm) among the investigated films. The superior performance of this film is attributed to the en-APTAS coupling-agent additive in the P3HT active layer concomitantly modifying the OH-functionalized substrate via a one-step spin-coating procedure. The increase in the abundance of adsorption sites in the channel region can induce more p-doping by NO2, leading to an increase of the hole carrier density and, thus, an increase of the current level in a p-type transistor gas sensor.