Influence of Mo+2 ion concentration on crystallization, microstructure, crystal imperfection and morphology of WO3 sprayed thin films

Abstract

Compositional dependence of microstructure and morphological properties of Mo _x W _1−x O _3 (0.2 ≥ x ≥ 0.0 at. %) thin films was studied. MoWO _3 films were deposited by chemical spray pyrolysis technique on pre-heated glass substrates at 400 °C and the sedimentation rate was kept constant at 70 ml min ^−1 with the deposition time fixed at 10 min to keep the film thickness constant at about 650 ± 5 nm. The prepared thin films were studied using x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive x-ray analysis (EDAX) techniques. The nature of the as-deposited films displayed by XRD showed beyond a reasonable doubt that they are amorphous. After thermal annealing at 500 °C for 2 h, all samples will be transferred to a polycrystalline having a triclinic structure. The microstructural parameters of the pure and doped samples were measured, using different methods and a comparison between them to determine the accuracy percentage of the measurement of these methods. The results also showed that the average crystallite size of the films decreased from 24 to 12 nm, on the contrary the internal microstrain increased from 23 × 10 ^−3 to 30 × 10 ^−3 with the addition of Mo element in WO _3 . Field emission scanning electron microscopy (FE-SEM) analysis also revealed that Mo dopant caused significant changes in the surface morphology of the films as well as an increase in particle size with increasing molybdenum concentration. The EDX results exhibited that the percentages of the isotropic elements Mo _x W _1−x O _3 agree well with those determined by atomic weight. In general, the results obtained in this study confirm that Mo _x W _1−x O _3 with these properties, is suitable for photovoltaic and optoelectronic applications.

Keywords

• spray pyrolysis
• thin films
• microstructure and surface morphology
• Mo doping WO3 thin films