Fabrication and Comprehensive Characterization of Cr2O3-Doped Polypyrrole Thin Films for Enhanced Ethanol Gas Sensing Applications

Abstract

Cr₂O₃-doped polypyrrole (PPy) thin films with 3.5, 5.5, and 7.5 wt.% loadings were fabricated on glass substrates using a simple drop-casting technique and comprehensively characterized. X-ray diffraction revealed improved crystallinity with doping, while FE-SEM and AFM showed clear surface evolution and larger effective surface area. Optical measurements indicated a progressive reduction of the bandgap from 2.83 eV (pure PPy) to 2.68 eV (7.5 wt.% Cr₂O₃), accompanied by enhanced electrical conductivity and carrier concentration confirmed by Hall and I–V analyses. Gas-sensing tests toward ethanol at room temperature demonstrated markedly improved performance: the 7.5 wt.% Cr₂O₃ film achieving a maximum sensitivity of approximately 12% at 200 ppm with faster response and recovery than pristine PPy. These findings show that controlled Cr₂O₃ incorporation tailors the structural, electronic, and surface features of PPy, making the films strong candidates for low-cost, high-performance ethanol sensors operating under ambient conditions.