Enhanced stability and performance of PEDOT:PSS films with bi-metallic nanoparticles for room-temperature ethanol gas sensors devices

This work presents the development of ethanol vapor sensors operating at room temperature, based on Poli(3,4-etilenodioxitiofeno) poliestireno sulfonato (PEDOT:PSS) films modified with bimetallic silver (Ag) and gold (Au) nanoparticles (Np) deposited in a multilayer structure. The devices made with the Ag-2/Au-3/PEDOT:PSS configuration showed superior performance, with a response of 43.1 %, response time of 48 s and recovery time of 78 s, compared to the pure PEDOT:PSS film, with a response of 40 %, 88 s and 132 s, respectively. Morphological analysis by Scanning Electron Microscopy indicated average particle sizes of 5.1 nm (Ag-2/Au-3) and 3.7 nm (Au⁻³/Ag⁻²), while UV-Vis spectroscopy revealed plasmon resonance peaks at 540 nm and 542 nm. X-ray diffraction confirmed the presence of crystalline Ag and Au phases. NEXAFS spectra at the sulphur K-edge revealed a longer electronic delocalization time for Ag⁻²/Au⁻³ (up to 10.15 fs), associated with the lower orientation of the PEDOT chain and, consequently, greater interaction with ethanol. Illumination with a 2 V white Light-Emitting Diode led to a 74 % increase in detection response and greater stability, with degradation of only 5 % after 10 cycles, compared to 17 % without illumination. Adopting a thermal route for nanoparticle synthesis, rather than the chemical route, resulted in a slight increase in sensory response, attributed to the reduction in particle size. The results highlight the bimetallic nanoparticles and plasmonic excitation in improving the sensitivity and stability of the sensors.