The role of TiO2 addition in ZnO nanocrystalline thin films: Variation of photoelectrochemical responsivity

Highlights: → (TiO2)x-(ZnO)1-x systems with different x values were synthesized by sol-gel method. → XRD showed a decrease in crystallinity of the systems by increasing x value. → AFM analysis revealed the highest roughness and surface area for the system with x = 10%. → This system showed highest photoresponse for water splitting and electrical resistance. - Abstract: In this study, the effects of TiO2 addition on the physical and photoelectrochemical properties of ZnO thin films have been investigated. The (TiO2)x-(ZnO)1-x nanocomposite thin films were dip-coated on both glass and indium tin oxide (ITO)-coated conducting glass substrates with various values of x, specifically 0, 0.05, 0.1, 0.25 and 0.5. Optical properties of the samples were studied by UV-vis spectrophotometry in the range of 300-1100 nm. The optical spectra of the nanocomposite thin films showed high transparency in the visible region. The optical bandgap energy of the (TiO2)x-(ZnO)1-x films increased slightly with increasing values of x. The crystalline structure of the nanocomposite films was investigated by X-ray diffraction, which indicated the formation of ZnO nanocrystals in the thin films with x < 0.5. Moreover, the crystallinity of the films decreased with increasing values of x. The surface chemical composition of the samples was investigated by X-ray photoelectron spectroscopy (XPS), which revealed stoichiometric ZnO and TiO2 on the surfaces of the films. The photoelectrochemical properties of the samples were also characterized using a high-pressure xenon light source and KOH electrolyte. The addition of 10 mol% (x = 0.1) TiO2 to the ZnO thin films resulted in the best photoresponse in the visible region of the solar spectrum. In addition, the effect of TiO2 concentration on the electrical properties and the flat-band potential of the (TiO2)x-(ZnO)1-x system was studied by impedance spectroscopy; x = 0.1 exhibited the highest donor density and charge-transfer resistance.