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

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-VO and BiVO. The V-rich region of the samples deposited under low and intermediate oxygen pressures was covered by VO longitudinal structures protruding from BiVO film. Higher oxygen pressure leads to the formation of BiVO@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 VO on the top of BiVO decreases its photoactivity, while the presence of a bulk BiVO@BiVO heterojunction is beneficial in water photooxidation.