Influence of Ag doping on structural, morphological, and optical characteristics of sol-gel spin-coated TiO2 thin films

Pure and Ag-doped Titanium dioxide (TiO₂) thin films have been synthesized via the sol-gel spin coating method, and their structural, morphological, and optical properties have been investigated. X-ray diffraction analysis verifies that the polycrystalline anatase TiO₂ phase is retained up to 2 % Ag doping. However, lattice expansion and grain refinement down to 25.345 nm are observed with increasing Ag content. Scanning electron microscopy (SEM) reveals the formation of large, isolated TiO₂ aggregates separated by drying-induced cracks across the film surface. Optical studies show the undoped TiO₂ films demonstrate excellent visible transparency (>75 % transmittance) that slightly decreases upon Ag doping, though it remains suitably high for device applications. Meanwhile, optical absorption and defect states improve with more Ag incorporation, narrowing the TiO₂ bandgap from 3.83 eV (undoped) to 3.51 eV (2 % Ag-doping) due to the incorporation of Ag-induced electronic states just below the conduction band minimum. The capability to control optical and structural properties through Ag doping highlights the potential of these TiO₂ films suitably tailored for photovoltaic devices or self-cleaning coatings.