Pulsed Laser Deposition of Bismuth Vanadate Thin Films—The Effect of Oxygen Pressure on the Morphology Composition and Photoelectrochemical Performance

摘要

Thin layers of bismuth vanadate were deposited using the pulsed laser deposition technique on commercially available FTO (fluorine-doped tin oxide) substrates. Films were sputtered from a sintered, monoclinic BiVO pellet, acting as the target, under various oxygen pressures (from 0.1 to 2 mbar), while the laser beam was perpendicular to the target surface and parallel to the FTO substrate. The oxygen pressure strongly affects the morphology and the composition of films observed as a Bi:V ratio gradient along the layer deposited on the substrate. Despite BiVO , two other phases were detected using XRD (X-ray diffraction) and Raman spectroscopy—V O and Bi V O . The V-rich region of the samples deposited under low and intermediate oxygen pressures was covered by V O longitudinal structures protruding from BiVO film. Higher oxygen pressure leads to the formation of Bi V O @BiVO bulk heterojunction. The presented results suggest that the ablation of the target leads to the plasma formation, where Bi and V containing ions can be spatially separated due to the interactions with oxygen molecules. In order to study the phenomenon more thoroughly, laser-induced breakdown spectroscopy measurements were performed. Then, obtained electrodes were used as photoanodes for photoelectrochemical water splitting. The highest photocurrent was achieved for films deposited under 1 mbar O pressure and reached 1 mA cm at about 0.8 V vs Ag/AgCl (3 M KCl). It was shown that V O on the top of BiVO decreases its photoactivity, while the presence of a bulk Bi V O @BiVO heterojunction is beneficial in water photooxidation.