Influence of molybdenum and chromium doping on WO3 thin films fabricated by spray pyrolysis: Structural and optical characterization

This study explores the structural, morphological, and optical evolution of WO₃ thin films doped with molybdenum (Mo) and chromium (Cr), fabricated by spray pyrolysis on glass and indium tin oxide (ITO)-coated glass substrates. Grazing incidence X-ray diffraction confirms that undoped WO₃ exhibits a monoclinic phase with average crystallite size ∼20 nm. Mo doping up to ∼1.83 at.% enhances crystallinity and maintains phase purity, whereas Cr doping (∼3.42 at.%) induces peak broadening, lattice strain, and crystallite size reduction to ∼14 nm. SEM and AFM investigations reveal that undoped WO₃ forms compact grains (∼50 nm) with smooth surfaces (Rₐ ≈ 24.6 nm), while moderate Mo doping (∼1.06 at.%) leads to porous nanostructures (∼100–120 nm) with decreased roughness (Rₐ ≈ 18.0 nm). Cr doping at ∼2.49 at.% induces anisotropic grain morphologies (nanorods/flakes), increased porosity, and peak surface roughness (Rₐ ≈ 39.3 nm). Raman analysis indicates dopant-induced redshifts and peak broadening linked to oxygen vacancy formation. Optical measurements show that Mo doping narrows the bandgap from 2.85 eV to ∼2.69 eV with increased transmittance (up to 67 %), while Cr doping reduces the bandgap to ∼2.44 eV but decreases transparency to ∼32 %. These results demonstrate that Mo and Cr dopants distinctly modulate WO₃ film properties, enabling tunability for use in gas sensing and electrochromic applications.