Structural, Optical, and Electrical Characterization of ZnO–MnO ₂ Composite Films for NO ₂ Gas Sensing Application

ZnO–MnO 2 composite thick films were fabricated via a screen‐printing technique to investigate the effect of MnO 2 concentration (1–11 wt.%) on structural, defect, electrical, and NO 2 gas sensing characteristics. X‐ray diffraction confirmed the preservation of the hexagonal wurtzite ZnO phase with the incorporation of MnO 2 secondary reflections without undesirable impurity phases. Controlled MnO 2 addition significantly influenced crystallite refinement, surface morphology, and defect‐related states. The 7 wt.% MnO 2 composition exhibited the smallest crystallite size (49.39 nm), maximum estimated specific surface area (4.01 m 2 /g), and enhanced porous microstructure. Optical analysis revealed bandgap modulation from 3.08 to 2.72 eV, indicating defect‐induced electronic structure modification. Electrical measurements demonstrated negative temperature coefficient behavior with optimized resistivity and moderate activation energy at 7 wt.% MnO 2 , favoring efficient charge transport modulation. Gas sensing evaluation showed a maximum sensitivity of 78.35% toward 700 ppm NO 2 at 120°C with rapid response (11s) and recovery (58s). The enhanced sensing performance is attributed to synergistic effects of crystallite refinement, defect‐induced band modulation, and improved adsorption–desorption kinetics at the ZnO–MnO 2 heterointerface. These findings demonstrate that controlled MnO 2 incorporation effectively tailors surface reactivity and charge transfer dynamics for low‐temperature NO 2 detection.